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https://dev.mysql.com/doc/refman/5.7/en/ansi-diff-foreign-keys.html
If ON UPDATE CASCADE or ON UPDATE SET NULL recurses to update the same table it has previously updated during the same cascade, it acts like RESTRICT. This means that you cannot use self-referential ON UPDATE CASCADE or ON UPDATE SET NULL operations. A self-referential ON DELETE SET NULL, on the other hand, is possible, as is a self-referential ON DELETE ...For example, if you define a RESTRICT type constraint, ...
https://dev.mysql.com/doc/refman/5.7/en/create-index.html
A UNIQUE index permits multiple NULL values for columns that can contain NULL. Otherwise, _rowid refers to the column in the first UNIQUE NOT NULL index if that index consists of a single integer column. If the first UNIQUE NOT NULL index does not ... CREATE [UNIQUE | FULLTEXT | SPATIAL] INDEX index_name [index_type] ON tbl_name (key_part,...) [index_option] [algorithm_option | lock_option] ...
https://dev.mysql.com/doc/refman/5.7/en/information-schema-optimization.html
row *************************** id: 1 select_type: SIMPLE table: VIEWS type: ALL possible_keys: NULL key: TABLE_SCHEMA,TABLE_NAME key_len: NULL ref: NULL rows: NULL Extra: Using where; Open_frm_only; Scanned 0 databases Use of constant database and ... Applications that monitor databases may make frequent use of INFORMATION_SCHEMA ...
https://dev.mysql.com/doc/refman/5.7/en/logical-operators.html
Table 12.5 Logical Operators Name Description AND, && Logical AND NOT, ! Negates value OR, || Logical OR XOR Logical XOR In SQL, all logical operators evaluate to TRUE, FALSE, or NULL (UNKNOWN). In MySQL, these are implemented as 1 (TRUE), 0 ...
https://dev.mysql.com/doc/refman/5.7/en/mysqldump.html
It is always enabled and attempting to disable it (--skip-secure-auth, --secure-auth=0) produces an error. NULL, 'NULL', and Empty Values: For a column named column_name, the NULL value, an empty string, and the string value 'NULL' are distinguished ... The mysqldump client utility performs logical backups, producing a set of SQL statements that can be executed to reproduce the original database object definitions and table ...
https://dev.mysql.com/doc/refman/5.7/en/spatial-operator-functions.html
ST_Buffer(g, d [, strategy1 [, strategy2 [, strategy3]]]) Returns a geometry that represents all points whose distance from the geometry value g is less than or equal to a distance of d, or NULL if any argument is NULL. If the argument is an empty ... OpenGIS proposes a number of functions that can produce ...
https://dev.mysql.com/doc/refman/5.7/en/load-xml.html
Suppose that we have a table named person, created as shown here: USE test; CREATE TABLE person ( person_id INT NOT NULL PRIMARY KEY, fname VARCHAR(40) NULL, lname VARCHAR(40) NULL, created TIMESTAMP ); Suppose further that this table is initially ...The tagname in the optional ROWS IDENTIFIED BY clause must also be given as a literal string, and must be surrounded by angle brackets (< and ...
https://dev.mysql.com/doc/refman/5.7/en/outer-join-simplification.html
Instead, MySQL converts the query to a query with no outer join operation if the WHERE condition is null-rejected. (That is, it converts the outer join to an inner join.) A condition is said to be null-rejected for an outer join operation if it ...
https://dev.mysql.com/doc/refman/5.7/en/spatial-convenience-functions.html
ST_Distance_Sphere(g1, g2 [, radius]) Returns the mimimum spherical distance between two points and/or multipoints on a sphere, in meters, or NULL if any geometry argument is NULL or empty. For example, this polygon is geometrically invalid: ... The ...
https://dev.mysql.com/doc/refman/5.7/en/aggregate-functions.html
COUNT(expr) Returns a count of the number of non-NULL values of expr in the rows retrieved by a SELECT statement. mysql> SELECT student.student_name,COUNT(*) FROM student,course WHERE student.student_id=course.student_id GROUP BY student_name; ...