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4 wrz 2018 · A composite index is only useful when you're combining the tests with AND, not OR. When you have an OR condition, it has to test each column independently, but a composite index is a tree that has all the values of DNIS within their related ANI. So you should create separate indexes for each column.
MySQL can create composite indexes (that is, indexes on multiple columns). An index may consist of up to 16 columns. For certain data types, you can index a prefix of the column (see Section 10.3.5, “Column Indexes”).
MySQL can create composite indexes (that is, indexes on multiple columns). An index may consist of up to 16 columns. For certain data types, you can index a prefix of the column (see Section 8.3.5, “Column Indexes” ).
The SQL statement below creates an index named "idx_lastname" on the "LastName" column in the "Persons" table: CREATE INDEX idx_lastname. ON Persons (LastName); If you want to create an index on a combination of columns, you can list the column names within the parentheses, separated by commas: CREATE INDEX idx_pname.
You can use this syntax to add an index and control the kind of index (HASH or BTREE). create index your_index_name on your_table_name(your_column_name) using HASH; or. create index your_index_name on your_table_name(your_column_name) using BTREE;
A composite index is an index on multiple columns. MySQL allows you to create a composite index that consists of up to 16 columns. A composite index is also known as a multiple-column index.
To create an index for a column or a list of columns, you specify the index name, the table to which the index belongs, and the column list. For example, to add a new index for the column c4, you use the following statement: CREATEINDEX idx_c4 ON t (c4);Code language:SQL (Structured Query Language)(sql)
