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https://dev.mysql.com/doc/refman/8.0/en/performance-schema-query-profiling.html
For example: mysql> SELECT * FROM employees.employees WHERE emp_no = 10001; +--------+------------+------------+-----------+--------+------------+ | emp_no | birth_date | first_name | last_name | gender | hire_date | ... The following example ...
https://dev.mysql.com/doc/refman/8.0/en/problems-with-float.html
If columns d1 and d2 had been defined as DECIMAL rather than DOUBLE, the result of the SELECT query would have contained only one row—the last one shown above. Suppose that you execute the following statements: CREATE TABLE t1(c1 FLOAT(53,0), c2 ... Floating-point numbers sometimes cause confusion because they are approximate and not stored as exact ...
https://dev.mysql.com/doc/refman/8.0/en/show-warnings.html
The LIMIT clause has the same syntax as for the SELECT statement. You can also retrieve this number from the warning_count system variable: SHOW COUNT(*) WARNINGS; SELECT @@warning_count; A difference in these statements is that the first is a ...
https://dev.mysql.com/doc/refman/8.0/en/sql-prepared-statements.html
Using prepared statements with placeholders for parameter values has the following benefits: Less overhead for parsing the statement each time it is executed. Typically, database applications process large volumes of almost-identical statements, ...
https://dev.mysql.com/doc/refman/8.0/en/stored-program-restrictions.html
This includes SELECT statements that do not have an INTO var_list clause and other statements such as SHOW, EXPLAIN, and CHECK TABLE. A function can process a result set either with SELECT ... (See also Bug #16522.) Each execution of the statements ...Some of the restrictions noted here apply to all stored routines; that is, both to stored procedures and stored ...
https://dev.mysql.com/doc/refman/8.0/en/view-syntax.html
A view can be created from many kinds of SELECT statements. The CREATE VIEW statement creates a new view (see Section 15.1.23, “CREATE VIEW Statement”). To alter the definition of a view or drop a view, use ALTER VIEW (see Section 15.1.11, ...
https://dev.mysql.com/doc/refman/8.0/en/ansi-diff-foreign-keys.html
For example, if you define a RESTRICT type constraint, and there is a child row with several parent rows, InnoDB does not permit the deletion of any of the parent rows. If ON UPDATE CASCADE or ON UPDATE SET NULL recurses to update the same table it ...
https://dev.mysql.com/doc/refman/8.0/en/charset-connection.html
If you do not say SET NAMES or SET CHARACTER SET, then for SELECT column1 FROM t, the server sends back all the values for column1 using the character set that the client specified when it connected. On the other hand, if you say SET NAMES 'latin1' ... A “connection” is what a client program makes when it connects to the server, to begin a session within which it interacts with the ...
https://dev.mysql.com/doc/refman/8.0/en/charset-unicode-utf8mb3.html
For example: CREATE TABLE t (s1 CHAR(1)) CHARACTER SET utf8mb3; SELECT * FROM t WHERE s1 COLLATE utf8mb3_general_ci = 'x'; DECLARE x VARCHAR(5) CHARACTER SET utf8mb3 COLLATE utf8mb3_danish_ci; SELECT CAST('a' AS CHAR CHARACTER SET utf8mb4) COLLATE ... The utf8mb3 character set has these characteristics: Supports BMP characters only (no support for supplementary characters) Requires a maximum of three bytes per multibyte ...
https://dev.mysql.com/doc/refman/8.0/en/comparisons-using-subqueries.html
WHERE 'a' = (SELECT column1 FROM t1) MySQL also permits this construct: non_subquery_operand LIKE (subquery) At one time the only legal place for a subquery was on the right side of a comparison, and you might still find some old DBMSs that insist ... The most common use of a subquery is in the form: non_subquery_operand comparison_operator (subquery) Where comparison_operator is one of these operators: = > < >= <= <> != <=> For example: ...