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https://dev.mysql.com/doc/refman/5.7/en/charset-metadata.html
Thus column names, database names, user names, version names, and most of the string results from SHOW are metadata. Otherwise, neither the SHOW statements nor SELECT statements for tables in INFORMATION_SCHEMA would work properly because different ... Metadata is “the data about the data.” Anything that describes the database—as opposed to being the contents of the database—is ...
https://dev.mysql.com/doc/refman/5.7/en/condition-filtering.html
In EXPLAIN output, the rows column indicates the row estimate for the chosen access method, and the filtered column reflects the effect of condition filtering. In such cases, these techniques may help: If a column is not indexed, index it so that ...
https://dev.mysql.com/doc/refman/5.7/en/correlated-subqueries.html
For example: SELECT * FROM t1 WHERE column1 = ANY (SELECT column1 FROM t2 WHERE t2.column2 = t1.column2); Notice that the subquery contains a reference to a column of t1, even though the subquery's FROM clause does not mention a table t1. Suppose ...
https://dev.mysql.com/doc/refman/5.7/en/counting-rows.html
Counting the total number of animals you have is the same question as “How many rows are in the pet table?” because there is one record per pet. COUNT(*) counts the number of rows, so the query to count your animals looks like this: mysql> ...
https://dev.mysql.com/doc/refman/5.7/en/example-foreign-keys.html
A foreign key relationship involves a parent table that holds the initial column values, and a child table with column values that reference the parent column values. This following example relates parent and child tables through a single-column ...
https://dev.mysql.com/doc/refman/5.7/en/extensions-to-ansi.html
Use of index names, indexes on a prefix of a column, and use of INDEX or KEY in CREATE TABLE statements. You don't need to name all selected columns in the GROUP BY clause. To perform case-sensitive comparisons instead, you should declare your ...
https://dev.mysql.com/doc/refman/5.7/en/faqs-mysql-cluster.html
You must also remember to account for any column indexes as follows: Each primary key or hash index created for an NDBCLUSTER table requires 21−25 bytes per record. Spatial indexes are not supported (although spatial columns can be used). This ...
https://dev.mysql.com/doc/refman/5.7/en/floating-point-types.html
A precision from 0 to 23 results in a 4-byte single-precision FLOAT column. A precision from 24 to 53 results in an 8-byte double-precision DOUBLE column. For example, a column defined as FLOAT(7,4) looks like -999.9999 when displayed. MySQL ... The ...
https://dev.mysql.com/doc/refman/5.7/en/fulltext-search.html
Full-text indexes can be used only with InnoDB or MyISAM tables, and can be created only for CHAR, VARCHAR, or TEXT columns. MATCH() takes a comma-separated list that names the columns to be searched. This rules out, for example, a table column ...
https://dev.mysql.com/doc/refman/5.7/en/identifier-case-sensitivity.html
The following statement would not work because it refers to a table both as my_table and as MY_TABLE: mysql> SELECT * FROM my_table WHERE MY_TABLE.col=1; Column, index, stored routine, and event names are not case-sensitive on any platform, nor are ... In MySQL, databases correspond to directories within the data ...