Each select_expr indicates a column that you want to retrieve. 每个select_expr表示要检索的列。There must be at least one select_expr.必须至少有一个select_expr。

table_references indicates the table or tables from which to retrieve rows. table_references表示要从中检索行的一个或多个表。Its syntax is described in Section 13.2.10.2, “JOIN Clause”.其语法在第13.2.10.2节，“JOIN子句”中描述。

SELECT supports explicit partition selection using the PARTITION clause with a list of partitions or subpartitions (or both) following the name of the table in a table_reference (see Section 13.2.10.2, “JOIN Clause”). SELECT支持使用PARTITION子句进行显式分区选择，PARTITION子句中的分区或子分区（或两者）列表位于table_reference中的表名称之后（请参阅第13.2.10.2节，“JOIN子句”）。In this case, rows are selected only from the partitions listed, and any other partitions of the table are ignored. 在这种情况下，只从列出的分区中选择行，而忽略表中的任何其他分区。For more information and examples, see Section 24.5, “Partition Selection”.有关更多信息和示例，请参阅第24.5节，“分区选择”。

The WHERE clause, if given, indicates the condition or conditions that rows must satisfy to be selected. WHERE子句（如果给定）表示要选择行必须满足的一个或多个条件。where_condition is an expression that evaluates to true for each row to be selected. where_condition是一个表达式，对于要选择的每一行，它的计算结果都为true。The statement selects all rows if there is no WHERE clause.如果没有WHERE子句，则语句将选择所有行。

In the WHERE expression, you can use any of the functions and operators that MySQL supports, except for aggregate (group) functions. 在WHERE表达式中，除了聚合（分组）函数之外，您可以使用MySQL支持的任何函数和运算符。See Section 9.5, “Expressions”, and Chapter 12, Functions and Operators.参见第9.5节，“表达式”和第12章，“函数和运算符”。

A select list consisting only of a single unqualified * can be used as shorthand to select all columns from all tables:仅由单个非限定*组成的选择列表可用作从所有表中选择所有列的缩写：

SELECT * FROM t1 INNER JOIN t2 ...

tbl_name.* can be used as a qualified shorthand to select all columns from the named table:可以用作从命名表中选择所有列的限定缩写：

SELECT t1.*, t2.* FROM t1 INNER JOIN t2 ...

If a table has invisible columns, * and tbl_name.* do not include them. 如果一个表有不可见的列，*和tbl_name.*不包括它们。To be included, invisible columns must be referenced explicitly.要包含不可见列，必须显式引用不可见列。

Use of an unqualified * with other items in the select list may produce a parse error. 将非限定*与选择列表中的其他项一起使用可能会产生分析错误。To avoid this problem, use a qualified tbl_name.* reference:为避免此问题，请使用限定的tbl_name.*引用：

SELECT AVG(score), t1.* FROM t1 ...

A select_expr can be given an alias using AS alias_name. select_expr可以使用AS alias_name来给定别名。The alias is used as the expression's column name and can be used in GROUP BY, ORDER BY, or HAVING clauses. 别名用作表达式的列名，可以在GROUP BY子句、ORDER BY子句或HAVING子句中使用。For example:例如：

SELECT CONCAT(last_name,', ',first_name) AS full_name
  FROM mytable ORDER BY full_name;

The AS keyword is optional when aliasing a select_expr with an identifier. 当用标识符为select_expr取别名时，AS关键字是可选的。The preceding example could have been written like this:前面的例子可以这样写：

SELECT CONCAT(last_name,', ',first_name) full_name
  FROM mytable ORDER BY full_name;

However, because the AS is optional, a subtle problem can occur if you forget the comma between two select_expr expressions: MySQL interprets the second as an alias name. 但是，由于AS是可选的，如果您忘记了两个select_expr之间的逗号，就会出现一个微妙的问题：MySQL将第二个表达式解释为别名。For example, in the following statement, columnb is treated as an alias name:例如，在以下语句中，columnb被视为别名：

SELECT columna columnb FROM mytable;

For this reason, it is good practice to be in the habit of using AS explicitly when specifying column aliases.因此，在指定列别名时，最好养成显式使用AS的习惯。

It is not permissible to refer to a column alias in a WHERE clause, because the column value might not yet be determined when the WHERE clause is executed. 不允许在WHERE子句中引用列别名，因为在执行WHERE子句时可能尚未确定列值。See Section B.3.4.4, “Problems with Column Aliases”.参见第B.3.4.4节，“列别名问题”。

The FROM table_references clause indicates the table or tables from which to retrieve rows. FROM table_references子句指示要从中检索行的一个或多个表。If you name more than one table, you are performing a join. 如果命名了多个表，则执行的是联接。For information on join syntax, see Section 13.2.10.2, “JOIN Clause”. 有关连接语法的信息，请参阅第13.2.10.2节，“连接子句”。For each table specified, you can optionally specify an alias.对于指定的每个表，可以选择指定别名。

tbl_name [[AS] alias] [index_hint]

The use of index hints provides the optimizer with information about how to choose indexes during query processing. 索引提示的使用为优化器提供了有关如何在查询处理期间选择索引的信息。For a description of the syntax for specifying these hints, see Section 8.9.4, “Index Hints”.有关指定这些提示的语法说明，请参阅第8.9.4节，“索引提示”。

You can use SET max_seeks_for_key=value as an alternative way to force MySQL to prefer key scans instead of table scans. 您可以使用SET max_seeks_for_key=value作为另一种方法，强制MySQL选择键扫描而不是表扫描。See Section 5.1.8, “Server System Variables”.请参阅第5.1.8节，“服务器系统变量”。

You can refer to a table within the default database as tbl_name, or as db_name.可以将默认数据库中的表引用为tbl_name或db_name。tbl_name to specify a database explicitly. tbl_name以显式指定数据库。You can refer to a column as col_name, tbl_name.col_name, or db_name.tbl_name.col_name. 可以将列引用为col_name、tbl_name.col_name或db_name.tbl_name.col_name。You need not specify a tbl_name or db_name.tbl_name prefix for a column reference unless the reference would be ambiguous. 不需要为列引用指定tbl_name或db_name.tbl_name前缀，除非引用不明确。See Section 9.2.2, “Identifier Qualifiers”, for examples of ambiguity that require the more explicit column reference forms.请参阅第9.2.2节“标识符限定符”，以了解需要更明确的列引用形式的歧义示例。

A table reference can be aliased using tbl_name AS alias_name or tbl_name alias_name. 表引用可以加别名，方法是使用tbl_name AS alias_name或tbl_name alias_name。These statements are equivalent:这些语句是等同的：

SELECT t1.name, t2.salary FROM employee AS t1, info AS t2
  WHERE t1.name = t2.name;

SELECT t1.name, t2.salary FROM employee t1, info t2
  WHERE t1.name = t2.name;

Columns selected for output can be referred to in ORDER BY and GROUP BY clauses using column names, column aliases, or column positions. 可以使用列名、列别名或列位置按ORDER BY和GROUP BY子句引用为输出选择的列。Column positions are integers and begin with 1:列位置是整数，从1开始：

SELECT college, region, seed FROM tournament
  ORDER BY region, seed;

SELECT college, region AS r, seed AS s FROM tournament
  ORDER BY r, s;

SELECT college, region, seed FROM tournament
  ORDER BY 2, 3;

To sort in reverse order, add the DESC (descending) keyword to the name of the column in the ORDER BY clause that you are sorting by. 若要按相反顺序排序，请将DESC（降序）关键字添加到排序依据的ORDER BY子句中列的名称中。The default is ascending order; this can be specified explicitly using the ASC keyword.默认为升序；这可以使用ASC关键字显式指定。

If ORDER BY occurs within a parenthesized query expression and also is applied in the outer query, the results are undefined and may change in a future version of MySQL.如果ORDER BY出现在带圆括号的查询表达式中，并且也应用于外部查询中，则结果是未定义的，可能会在MySQL的未来版本中更改。

Use of column positions is deprecated because the syntax has been removed from the SQL standard.不赞成使用列位置，因为该语法已从SQL标准中删除。

Prior to MySQL 8.0.13, MySQL supported a nonstandard syntax extension that permitted explicit ASC or DESC designators for GROUP BY columns. 在MySQL 8.0.13之前，MySQL支持一个非标准的语法扩展，该扩展允许对GROUP BY列使用显式ASC或DESC指示符。MySQL 8.0.12 and later supports ORDER BY with grouping functions so that use of this extension is no longer necessary. MySQL 8.0.12及更高版本支持ORDER BY配合分组函数，因此不再需要使用此扩展。(Bug #86312, Bug #26073525) This also means you can sort on an arbitrary column or columns when using GROUP BY, like this:这也意味着您可以在使用GROUP BY时对任意列进行排序，如下所示：

SELECT a, b, COUNT(c) AS t FROM test_table GROUP BY a,b ORDER BY a,t DESC;

As of MySQL 8.0.13, the GROUP BY extension is no longer supported: ASC or DESC designators for GROUP BY columns are not permitted.从MySQL 8.0.13开始，不再支持GROUP BY扩展：不允许使用ASC或DESC指示符来表示GROUP BY列。

When you use ORDER BY or GROUP BY to sort a column in a SELECT, the server sorts values using only the initial number of bytes indicated by the max_sort_length system variable.使用ORDER BY或GROUP BY对SELECT中的列进行排序时，服务器仅使用max_sort_length系统变量指示的初始字节数对值进行排序。

MySQL extends the use of GROUP BY to permit selecting fields that are not mentioned in the GROUP BY clause. MySQL扩展了GROUP BY的使用，允许选择GROUP BY子句中没有提到的字段。If you are not getting the results that you expect from your query, please read the description of GROUP BY found in Section 12.20, “Aggregate Functions”.如果您没有从查询中得到预期的结果，请阅读第12.20节，“聚合函数”中的GROUP BY说明。

GROUP BY permits a WITH ROLLUP modifier. GROUP BY允许使用ROLLUP修饰符。See Section 12.20.2, “GROUP BY Modifiers”.请参阅第12.20.2节，“GROUP BY修饰符”。

Previously, it was not permitted to use ORDER BY in a query having a WITH ROLLUP modifier. 以前，不允许在具有WITH ROLLUP修饰符的查询中使用ORDER BY。This restriction is lifted as of MySQL 8.0.12. 从MySQL 8.0.12开始，这个限制就被取消了。See Section 12.20.2, “GROUP BY Modifiers”.见第12.20.2节，“按修改器分组”。

The HAVING clause, like the WHERE clause, specifies selection conditions. HAVING子句与WHERE子句一样，指定了选择条件。The WHERE clause specifies conditions on columns in the select list, but cannot refer to aggregate functions. WHERE子句指定了选择列表中列的条件，但不能引用聚合函数。The HAVING clause specifies conditions on groups, typically formed by the GROUP BY clause. HAVING子句指定组的条件，通常由GROUP BY子句组成。The query result includes only groups satisfying the HAVING conditions. 查询结果只包括满足HAVING条件的组。(If no GROUP BY is present, all rows implicitly form a single aggregate group.)（如果不存在GROUP BY，则所有行都隐式地形成一个聚合组。）

The HAVING clause is applied nearly last, just before items are sent to the client, with no optimization. HAVING子句几乎是最后应用的，就在项目发送到客户机之前，没有进行优化。(LIMIT is applied after HAVING.)（LIMIT在HAVING后应用。）

The SQL standard requires that HAVING must reference only columns in the GROUP BY clause or columns used in aggregate functions. SQL标准要求HAVING必须只引用GROUP BY子句中的列或聚合函数中使用的列。However, MySQL supports an extension to this behavior, and permits HAVING to refer to columns in the SELECT list and columns in outer subqueries as well.但是，MySQL支持对这种行为的扩展，并允许HAVING引用SELECT列表中的列和外部子查询中的列。

If the HAVING clause refers to a column that is ambiguous, a warning occurs. 如果HAVING子句引用的列不明确，则会出现警告。In the following statement, col2 is ambiguous because it is used as both an alias and a column name:在下面的语句中，col2是不明确的，因为它同时用作别名和列名：

SELECT COUNT(col1) AS col2 FROM t GROUP BY col2 HAVING col2 = 2;

Preference is given to standard SQL behavior, so if a HAVING column name is used both in GROUP BY and as an aliased column in the select column list, preference is given to the column in the GROUP BY column.首选标准SQL行为，因此如果HAVING列名在GROUP BY和选择列列表中用作别名列，则首选GROUP BY列中的列。

Do not use HAVING for items that should be in the WHERE clause. 对于应该在WHERE子句中的项，不要使用HAVING。For example, do not write the following:例如，不要写以下内容：

SELECT col_name FROM tbl_name HAVING col_name > 0;

Write this instead:改为这样写：

SELECT col_name FROM tbl_name WHERE col_name > 0;

The HAVING clause can refer to aggregate functions, which the WHERE clause cannot:HAVING子句可以引用聚合函数，WHERE子句不能：

SELECT user, MAX(salary) FROM users
  GROUP BY user HAVING MAX(salary) > 10;

(This did not work in some older versions of MySQL.)（这在MySQL的一些旧版本中不起作用。）

MySQL permits duplicate column names. MySQL允许重复的列名。That is, there can be more than one select_expr with the same name. 也就是说，可以有多个具有相同名称的select_expr。This is an extension to standard SQL. 这是对标准SQL的扩展。Because MySQL also permits GROUP BY and HAVING to refer to select_expr values, this can result in an ambiguity:因为MySQL还允许GROUP BY和HAVING引用select_expr值，这可能会导致歧义：

SELECT 12 AS a, a FROM t GROUP BY a;

In that statement, both columns have the name a. 在该语句中，两列的名称都是a。To ensure that the correct column is used for grouping, use different names for each select_expr.为确保使用正确的列进行分组，请为每个select_expr使用不同的名称。

The WINDOW clause, if present, defines named windows that can be referred to by window functions. WINDOW子句（如果存在）定义了可由窗口函数引用的命名窗口。For details, see Section 12.21.4, “Named Windows”.有关详细信息，请参阅第12.21.4节，“命名窗口”。

MySQL resolves unqualified column or alias references in ORDER BY clauses by searching in the select_expr values, then in the columns of the tables in the FROM clause. MySQL在ORDER BY子句中解析非限定列或别名引用，方法是先搜索select_expr值，然后搜索FROM子句中表的列。For GROUP BY or HAVING clauses, it searches the FROM clause before searching in the select_expr values. 对于GROUP BY或HAVING子句，它先搜索FROM子句，然后再搜索select_expr值。(For GROUP BY and HAVING, this differs from the pre-MySQL 5.0 behavior that used the same rules as for ORDER BY.)（对于GROUP BY和HAVING，这与MySQL5.0之前的行为不同，后者使用与ORDER BY相同的规则。）

The LIMIT clause can be used to constrain the number of rows returned by the SELECT statement. LIMIT子句可用于约束SELECT语句返回的行数。LIMIT takes one or two numeric arguments, which must both be nonnegative integer constants, with these exceptions:LIMIT接受一个或两个数值参数，这两个参数都必须是非负整数常量，但有以下例外：

With two arguments, the first argument specifies the offset of the first row to return, and the second specifies the maximum number of rows to return. 对于两个参数，第一个参数指定要返回的第一行的偏移量，第二个参数指定要返回的最大行数。The offset of the initial row is 0 (not 1):初始行的偏移量为0（不是1)：

SELECT * FROM tbl LIMIT 5,10;  # Retrieve rows 6-15

To retrieve all rows from a certain offset up to the end of the result set, you can use some large number for the second parameter. 要检索从某个偏移量到结果集末尾的所有行，可以使用一些大的数字作为第二个参数。This statement retrieves all rows from the 96th row to the last:此语句检索从第96行到最后一行的所有行：

SELECT * FROM tbl LIMIT 95,18446744073709551615;

With one argument, the value specifies the number of rows to return from the beginning of the result set:对于一个参数，该值指定从结果集开头返回的行数：

SELECT * FROM tbl LIMIT 5;     # Retrieve first 5 rows

In other words, LIMIT row_count is equivalent to LIMIT 0, row_count.换句话说，LIMIT row_count等同于LIMIT 0, row_count。

For prepared statements, you can use placeholders. 对于准备好的语句，可以使用占位符。The following statements return one row from the tbl table:以下语句从tbl表返回一行：

SET @a=1;
PREPARE STMT FROM 'SELECT * FROM tbl LIMIT ?';
EXECUTE STMT USING @a;

The following statements return the second to sixth rows from the tbl table:以下语句返回tbl表的第二到第六行：

SET @skip=1; SET @numrows=5;
PREPARE STMT FROM 'SELECT * FROM tbl LIMIT ?, ?';
EXECUTE STMT USING @skip, @numrows;

For compatibility with PostgreSQL, MySQL also supports the LIMIT row_count OFFSET offset syntax.为了与PostgreSQL兼容，MySQL还支持LIMIT row_count OFFSET offset语法。

If LIMIT occurs within a parenthesized query expression and also is applied in the outer query, the results are undefined and may change in a future version of MySQL.如果LIMIT出现在带圆括号的查询表达式中，并且也应用在外部查询中，那么结果将是未定义的，并且可能在MySQL的未来版本中更改。

The SELECT ... INTO form of SELECT enables the query result to be written to a file or stored in variables. SELECT的SELECT ... INTO的形式可以将查询结果写入文件或存储在变量中。For more information, see Section 13.2.10.1, “SELECT ... INTO Statement”.有关更多信息，请参阅第13.2.10.1节，“SELECT ... INTO语句”。

If you use FOR UPDATE with a storage engine that uses page or row locks, rows examined by the query are write-locked until the end of the current transaction.如果对使用页锁或行锁的存储引擎使用FOR UPDATE，则查询检查的行将被写锁定，直到当前事务结束。

You cannot use FOR UPDATE as part of the SELECT in a statement such as CREATE TABLE new_table SELECT ... FROM old_table .... 在诸如CREATE TABLE new_table SELECT ... FROM old_table ...之类的语句中，不能将FOR UPDATE用作SELECT的一部分。(If you attempt to do so, the statement is rejected with the error Can't update table 'old_table' while 'new_table' is being created.)（如果您尝试这样做，则会拒绝该语句，理由为Can't update table 'old_table' while 'new_table' is being created。）

FOR SHARE and LOCK IN SHARE MODE set shared locks that permit other transactions to read the examined rows but not to update or delete them. FOR SHARE和LOCK IN SHARE MODE设置共享锁，允许其他事务读取检查的行，但不能更新或删除它们。FOR SHARE and LOCK IN SHARE MODE are equivalent. FOR SHARE和LOCK IN SHARE MODE是等效的。However, FOR SHARE, like FOR UPDATE, supports NOWAIT, SKIP LOCKED, and OF tbl_name options. 但是，FOR SHARE和FOR UPDATE一样，支持NOWAIT、SKIP LOCKED和OF tbl_name选项。FOR SHARE is a replacement for LOCK IN SHARE MODE, but LOCK IN SHARE MODE remains available for backward compatibility.FOR SHARE是LOCK IN SHARE MODE的替代品，但LOCK IN SHARE MODE仍可用于向后兼容。

NOWAIT causes a FOR UPDATE or FOR SHARE query to execute immediately, returning an error if a row lock cannot be obtained due to a lock held by another transaction.NOWAIT导致FOR UPDATE或FOR SHARE查询立即执行，如果由于另一个事务持有的锁而无法获取行锁，则返回错误。

SKIP LOCKED causes a FOR UPDATE or FOR SHARE query to execute immediately, excluding rows from the result set that are locked by another transaction.SKIP LOCKED导致FOR UPDATE或FOR SHARE查询立即执行，排除结果集中被另一个事务锁定的行。

NOWAIT and SKIP LOCKED options are unsafe for statement-based replication.NOWAIT和SKIP LOCKED选项对于基于语句的复制不安全。

OF tbl_name applies FOR UPDATE and FOR SHARE queries to named tables. For example:OF tbl_name应用于对命名表的FOR UPDATE和FOR SHARE查询。例如：

SELECT * FROM t1, t2 FOR SHARE OF t1 FOR UPDATE OF t2;

All tables referenced by the query block are locked when OF tbl_name is omitted. 如果省略了OF tbl_name，则查询块引用的所有表都将被锁定。Consequently, using a locking clause without OF tbl_name in combination with another locking clause returns an error. 因此，将一个不带OF tbl_name的锁定子句与另一个锁定子句结合使用会返回错误。Specifying the same table in multiple locking clauses returns an error. 在多个锁定子句中指定同一个表将返回错误。If an alias is specified as the table name in the SELECT statement, a locking clause may only use the alias. 如果在SELECT语句中将别名指定为表名，则锁定子句只能使用别名。If the SELECT statement does not specify an alias explicitly, the locking clause may only specify the actual table name.如果SELECT语句没有显式指定别名，那么锁定子句只能指定实际的表名。

For more information about FOR UPDATE and FOR SHARE, see Section 15.7.2.4, “Locking Reads”. 有关FOR UPDATE和FOR SHARE的更多信息，请参阅第15.7.2.4节，“锁定读取”。For additional information about NOWAIT and SKIP LOCKED options, see Locking Read Concurrency with NOWAIT and SKIP LOCKED.有关NOWAIT和SKIP LOCKED选项的更多信息，请参阅使用NOWAIT和SKIP LOCKED锁定读取并发。

The ALL and DISTINCT modifiers specify whether duplicate rows should be returned. ALL和DISTINCT修饰符指定是否应返回重复的行。ALL (the default) specifies that all matching rows should be returned, including duplicates. ALL（默认值）指定应返回所有匹配的行，包括重复的行。DISTINCT specifies removal of duplicate rows from the result set. DISTINCT指定从结果集中删除重复行。It is an error to specify both modifiers. 指定两个修饰符都是错误的。DISTINCTROW is a synonym for DISTINCT.DISTINCTROW是DISTINCT的同义词。

In MySQL 8.0.12 and later, DISTINCT can be used with a query that also uses WITH ROLLUP. 在MySQL8.0.12及更高版本中，DISTINCT可以与同样使用ROLLUP的查询一起使用。(Bug #87450, Bug #26640100)

HIGH_PRIORITY gives the SELECT higher priority than a statement that updates a table. HIGH_PRIORITY赋予SELECT比更新表的语句更高的优先级。You should use this only for queries that are very fast and must be done at once. 您应该仅将其用于非常快速且必须立即完成的查询。A SELECT HIGH_PRIORITY query that is issued while the table is locked for reading runs even if there is an update statement waiting for the table to be free. 在锁定表以进行读取时发出的SELECT HIGH_PRIORITY查询，即使有更新语句等待表释放，也会运行该查询。This affects only storage engines that use only table-level locking (such as MyISAM, MEMORY, and MERGE).这只影响仅使用表级锁定的存储引擎（如MyISAM、MEMORY和MERGE）。

HIGH_PRIORITY cannot be used with SELECT statements that are part of a UNION.HIGH_PRIORITY不能与属于联合的SELECT语句一起使用。

STRAIGHT_JOIN forces the optimizer to join the tables in the order in which they are listed in the FROM clause. STRAIGHT_JOIN强制优化器按照表在FROM子句中列出的顺序连接这些表。You can use this to speed up a query if the optimizer joins the tables in nonoptimal order. 如果优化器以非最佳顺序联接表，则可以使用此选项加快查询速度。STRAIGHT_JOIN also can be used in the table_references list. 在table_references列表中也可以使用STRAIGHT_JOIN。See Section 13.2.10.2, “JOIN Clause”.请参阅第13.2.10.2节，“JOIN子句”。

STRAIGHT_JOIN does not apply to any table that the optimizer treats as a const or system table. STRAIGHT_JOIN不适用于优化器视为const表或system表的任何表。Such a table produces a single row, is read during the optimization phase of query execution, and references to its columns are replaced with the appropriate column values before query execution proceeds. 这样的表生成一行，在查询执行的优化阶段读取，在查询执行继续之前，对其列的引用被替换为适当的列值。These tables appear first in the query plan displayed by EXPLAIN. 这些表首先出现在EXPLAIN显示的查询计划中。See Section 8.8.1, “Optimizing Queries with EXPLAIN”. 请参阅第8.8.1节，“使用EXPLAIN优化查询”。This exception may not apply to const or system tables that are used on the NULL-complemented side of an outer join (that is, the right-side table of a LEFT JOIN or the left-side table of a RIGHT JOIN.此异常可能不适用于在外部联接的NULL补边上使用的const表或system表（即，LEFT JOIN的右侧表或RIGHT JOIN的左侧表）。

SQL_BIG_RESULT or SQL_SMALL_RESULT can be used with GROUP BY or DISTINCT to tell the optimizer that the result set has many rows or is small, respectively. SQL_BIG_RESULT或SQL_SMALL_RESULT可与GROUP BY或DISTINCT一起使用，以告诉优化器结果集分别有多行或小行。For SQL_BIG_RESULT, MySQL directly uses disk-based temporary tables if they are created, and prefers sorting to using a temporary table with a key on the GROUP BY elements. 对于SQL_BIG_RESULT，MySQL直接使用基于磁盘的临时表（如果创建了临时表），并且更喜欢排序，而不是使用在GROUP BY元素上带有键的临时表。For SQL_SMALL_RESULT, MySQL uses in-memory temporary tables to store the resulting table instead of using sorting. 对于SQL_SMALL_RESULT，MySQL使用内存中的临时表来存储生成的表，而不是使用排序。This should not normally be needed.这通常不需要。

SQL_BUFFER_RESULT forces the result to be put into a temporary table. SQL_BUFFER_RESULT强制将结果放入临时表中。This helps MySQL free the table locks early and helps in cases where it takes a long time to send the result set to the client. 这有助于MySQL尽早释放表锁，并在需要很长时间才能将结果集发送到客户端的情况下提供帮助。This modifier can be used only for top-level SELECT statements, not for subqueries or following UNION.此修饰符只能用于顶级SELECT语句，不能用于子查询或后续UNION。

SQL_CALC_FOUND_ROWS tells MySQL to calculate how many rows there would be in the result set, disregarding any LIMIT clause. SQL_CALC_FOUND_ROWS告诉MySQL计算结果集中将有多少行，而忽略任何LIMIT子句。The number of rows can then be retrieved with SELECT FOUND_ROWS(). 然后可以使用SELECT FOUND_rows()检索行数。See Section 12.16, “Information Functions”.见第12.16节，“信息函数”。

The SQL_CACHE and SQL_NO_CACHE modifiers were used with the query cache prior to MySQL 8.0. 在MySQL 8.0之前的查询缓存中使用了SQL_CACHE和SQL_NO_CACHE修饰符。The query cache was removed in MySQL 8.0. 在MySQL 8.0中删除了查询缓存。The SQL_CACHE modifier was removed as well. SQL_CACHE修饰符也被删除。SQL_NO_CACHE is deprecated, and has no effect; expect it to be removed in a future MySQL release.SQL_NO_CACHE已弃用，并且没有效果；希望在将来的MySQL版本中删除它。