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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”).
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 ON Persons (LastName, FirstName);
Two Column Index. create table t1 ( accountid tinyint, logindate date); create index idx on t1 (accountid, logindate);
key_part2, ...) creates an index with multiple key parts. Index key values are formed by concatenating the values of the given key parts. For example (col1, col2, col3) specifies a multiple-column index with index keys consisting of values from col1, col2, and col3.
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: CREATE INDEX idx_c4 ON t(c4); Code language: SQL (Structured Query Language) (sql)
10.3.1 How MySQL Uses Indexes. Indexes are used to find rows with specific column values quickly. Without an index, MySQL must begin with the first row and then read through the entire table to find the relevant rows. The larger the table, the more this costs. If the table has an index for the columns in question, MySQL can quickly determine ...
