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22 lis 2010 · To add an index to a table without a lock resulting on UPDATE/ INSERT, the following statement format can be used: ALTER TABLE my_table ADD INDEX my_table__idx (my_column), ALGORITHM=INPLACE, LOCK=NONE;
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;
CREATE INDEX enables you to add indexes to existing tables. CREATE INDEX is mapped to an ALTER TABLE statement to create indexes. See Section 15.1.9, “ALTER TABLE Statement”. CREATE INDEX cannot be used to create a PRIMARY KEY; use ALTER TABLE instead.
So, in general, indexing creates a tradeoff between read efficiency and write efficiency. With no indexes, inserts can be very fast -- the database engine just adds a row to the table. As you add indexes, the engine must update each index while performing the insert. On the other hand, reads become a lot faster.
The CREATE INDEX statement is used to create indexes in tables. Indexes are used to retrieve data from the database more quickly than otherwise. The users cannot see the indexes, they are just used to speed up searches/queries.
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 ...
19 wrz 2012 · SELECT COUNT(1) IndexIsThere FROM INFORMATION_SCHEMA.STATISTICS WHERE table_schema=DATABASE() AND table_name='mytable' AND index_name='index_name'; If IndexIsThere is 0, you can create in the index. Perhaps you can write a stored procedure to create an index on the table of your choice.
