13.2.10 SELECT Syntax

Each select_expr indicates a column that you want to retrieve. There must be at least one select_expr.

table_references indicates the table or tables from which to retrieve rows. Its syntax is described in Section 13.2.10.2, “JOIN Syntax”.

SELECT supports explicit partition selection using the PARTITION 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 Syntax”). In this case, rows are selected only from the partitions listed, and any other partitions of the table are ignored. For more information and examples, see Section 23.5, “Partition Selection”.

SELECT ... PARTITION from tables using storage engines such as MyISAM that perform table-level locks (and thus partition locks) lock only the partitions or subpartitions named by the PARTITION option.

For more information, see Partitioning and Locking.

The WHERE clause, if given, indicates the condition or conditions that rows must satisfy to be selected. where_condition is an expression that evaluates to true for each row to be selected. The statement selects all rows if there is no WHERE clause.

In the WHERE expression, you can use any of the functions and operators that MySQL supports, except for aggregate (summary) functions. See Section 9.5, “Expressions”, and Chapter 12, Functions and Operators.

A select list consisting only of a single unqualified * can be used as shorthand to select all columns from all tables:

tbl_name.* can be used as a qualified shorthand to select all columns from the named table:

Use of an unqualified * with other items in the select list may produce a parse error. To avoid this problem, use a qualified tbl_name.* reference

A select_expr can be given an alias using AS alias_name. The alias is used as the expression's column name and can be used in GROUP BY, ORDER BY, or HAVING clauses. For example:

The AS keyword is optional when aliasing a select_expr with an identifier. The preceding example could have been written like this:

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. For example, in the following statement, columnb is treated as an alias name:

For this reason, it is good practice to be in the habit of using AS explicitly when specifying column aliases.

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. See Section B.5.4.4, “Problems with Column Aliases”.

The FROM table_references clause indicates the table or tables from which to retrieve rows. If you name more than one table, you are performing a join. For information on join syntax, see Section 13.2.10.2, “JOIN Syntax”. For each table specified, you can optionally specify an alias.

The use of index hints provides the optimizer with information about how to choose indexes during query processing. For a description of the syntax for specifying these hints, see Section 8.9.4, “Index Hints”.

You can use SET max_seeks_for_key=value as an alternative way to force MySQL to prefer key scans instead of table scans. See Section 5.1.8, “Server System Variables”.

You can refer to a table within the default database as tbl_name, or as db_name.tbl_name to specify a database explicitly. You can refer to a column as col_name, tbl_name.col_name, or 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. See Section 9.2.1, “Identifier Qualifiers”, for examples of ambiguity that require the more explicit column reference forms.

A table reference can be aliased using tbl_name AS alias_name or tbl_name alias_name:

Columns selected for output can be referred to in ORDER BY and GROUP BY clauses using column names, column aliases, or column positions. Column positions are integers and begin with 1:

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. The default is ascending order; this can be specified explicitly using the ASC keyword.

If ORDER BY occurs within a subquery and also is applied in the outer query, the outermost ORDER BY takes precedence. For example, results for the following statement are sorted in descending order, not ascending order:

Use of column positions is deprecated because the syntax has been removed from the SQL standard.

Prior to MySQL 8.0.13, MySQL supported a nonstandard syntax extension that permitted explicit ASC or DESC designators for GROUP BY columns. MySQL 8.0.12 and later supports ORDER BY with grouping functions so that use of this extension is no longer necessary. (Bug #86312, Bug #26073525) This also means you can sort on an arbitrary column or columns when using GROUP BY, like this:

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.

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.

MySQL extends the use of GROUP BY to permit selecting fields that are not mentioned in the GROUP BY clause. 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 (GROUP BY) Functions”.

GROUP BY permits a WITH ROLLUP modifier. See Section 12.20.2, “GROUP BY Modifiers”.

Previously, it was not permitted to use ORDER BY in a query having a WITH ROLLUP modifier. This restriction is lifted as of MySQL 8.0.12. See Section 12.20.2, “GROUP BY Modifiers”.

The HAVING clause is applied nearly last, just before items are sent to the client, with no optimization. (LIMIT is applied after HAVING.)

The SQL standard requires that HAVING must reference only columns in the GROUP BY clause or columns used in aggregate functions. 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.

If the HAVING clause refers to a column that is ambiguous, a warning occurs. In the following statement, col2 is ambiguous because it is used as both an alias and a column name:

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 output column list, preference is given to the column in the GROUP BY column.

Do not use HAVING for items that should be in the WHERE clause. For example, do not write the following:

Write this instead:

The HAVING clause can refer to aggregate functions, which the WHERE clause cannot:

(This did not work in some older versions of MySQL.)

MySQL permits duplicate column names. That is, there can be more than one select_expr with the same name. This is an extension to standard SQL. Because MySQL also permits GROUP BY and HAVING to refer to select_expr values, this can result in an ambiguity:

In that statement, both columns have the name a. To ensure that the correct column is used for grouping, use different names for each select_expr.

The WINDOW clause, if present, defines named windows that can be referred to by window functions. For details, see Section 12.21.4, “Named Windows”.

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. For GROUP BY or HAVING clauses, it searches the FROM clause before searching in the select_expr values. (For GROUP BY and HAVING, this differs from the pre-MySQL 5.0 behavior that used the same rules as for ORDER BY.)

The LIMIT clause can be used to constrain the number of rows returned by the SELECT statement. LIMIT takes one or two numeric arguments, which must both be nonnegative integer constants, with these exceptions:

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. The offset of the initial row is 0 (not 1):

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. This statement retrieves all rows from the 96th row to the last:

With one argument, the value specifies the number of rows to return from the beginning of the result set:

In other words, LIMIT row_count is equivalent to LIMIT 0, row_count.

For prepared statements, you can use placeholders. The following statements will return one row from the tbl table:

The following statements will return the second to sixth row from the tbl table:

For compatibility with PostgreSQL, MySQL also supports the LIMIT row_count OFFSET offset syntax.

If LIMIT occurs within a subquery and also is applied in the outer query, the outermost LIMIT takes precedence. For example, the following statement produces two rows, not one:

The SELECT ... INTO form of SELECT enables the query result to be written to a file or stored in variables. For more information, see Section 13.2.10.1, “SELECT ... INTO Syntax”.

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.

You cannot use FOR UPDATE as part of the SELECT in a statement such as CREATE TABLE new_table SELECT ... FROM old_table .... (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.)

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 and LOCK IN SHARE MODE are equivalent. However, FOR SHARE, like FOR UPDATE, supports NOWAIT, SKIP LOCKED, and OF tbl_name options. FOR SHARE is a replacement for LOCK IN SHARE MODE, but LOCK IN SHARE MODE remains available for backward compatibility.

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.

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.

NOWAIT and SKIP LOCKED options are unsafe for statement-based replication.

OF tbl_name applies FOR UPDATE and FOR SHARE queries to named tables. For example:

All tables referenced by the query block are locked when OF tbl_name is omitted. Consequently, using a locking clause without OF tbl_name in combination with another locking clause returns an error. Specifying the same table in multiple locking clauses returns an error. If an alias is specified as the table name in the SELECT statement, a locking clause may only use the alias. If the SELECT statement does not specify an alias explicitly, the locking clause may only specify the actual table name.

For more information about FOR UPDATE and FOR SHARE, see Section 15.7.2.4, “Locking Reads”. For additional information about NOWAIT and SKIP LOCKED options, see Locking Read Concurrency with NOWAIT and SKIP LOCKED.

The ALL and DISTINCT modifiers specify whether duplicate rows should be returned. ALL (the default) specifies that all matching rows should be returned, including duplicates. DISTINCT specifies removal of duplicate rows from the result set. It is an error to specify both modifiers. DISTINCTROW is a synonym for DISTINCT.

In MySQL 8.0.12 and later, DISTINCT can be used with a query that also uses WITH ROLLUP. (Bug #87450, Bug #26640100)

HIGH_PRIORITY gives the SELECT higher priority than a statement that updates a table. You should use this only for queries that are very fast and must be done at once. 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. This affects only storage engines that use only table-level locking (such as MyISAM, MEMORY, and MERGE).

HIGH_PRIORITY cannot be used with SELECT statements that are part of a UNION.

STRAIGHT_JOIN forces the optimizer to join the tables in the order in which they are listed in the FROM clause. You can use this to speed up a query if the optimizer joins the tables in nonoptimal order. STRAIGHT_JOIN also can be used in the table_references list. See Section 13.2.10.2, “JOIN Syntax”.

STRAIGHT_JOIN does not apply to any table that the optimizer treats as a const or system table. 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. These tables will appear first in the query plan displayed by EXPLAIN. See Section 8.8.1, “Optimizing Queries with EXPLAIN”. 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.

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. 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. For SQL_SMALL_RESULT, MySQL uses in-memory temporary tables to store the resulting table instead of using sorting. This should not normally be needed.

SQL_BUFFER_RESULT forces the result to be put into a temporary table. 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. This modifier can be used only for top-level SELECT statements, not for subqueries or following UNION.

SQL_CALC_FOUND_ROWS tells MySQL to calculate how many rows there would be in the result set, disregarding any LIMIT clause. The number of rows can then be retrieved with SELECT FOUND_ROWS(). See Section 12.15, “Information Functions”.

The SQL_CACHE and SQL_NO_CACHE modifiers were used with the query cache prior to MySQL 8.0. The query cache was removed in MySQL 8.0. The SQL_CACHE modifier was removed as well. SQL_NO_CACHE is deprecated, has no effect, and will be removed in a future MySQL release.