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I have a table "data" with column id(varchar), text(varchar), date(date). Creating index on mysql, I use heidiSQL.
When I right click on the column and select create new index (key), the code shows it's using alter table data add index 'index1' ('id,date(10)')
What is the difference between this and create index index1 on data ('id,date(10)')
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Index: It is a schema object which is used to provide improved performance in the retrieval of rows from a table. Unique Index: Unique indexes guarantee that no two rows of a table have duplicate values in the key column (or columns).
MySQL has three types of indexes: INDEX, UNIQUE (which requires each row to have a unique value), and PRIMARY KEY (which is just a particular UNIQUE index).
In MySQL, an index can be created on a table when the table is created with CREATE TABLE command. Otherwise, CREATE INDEX enables to add indexes to existing tables. A multiple-column index can be created using multiple columns. The indexes are formed by concatenating the values of the given columns.
ALTER command to add and drop INDEX ALTER TABLE tbl_name ADD INDEX index_name (column_list) − This adds an ordinary index in which any value may appear more than once. ALTER TABLE tbl_name ADD FULLTEXT index_name (column_list) − This creates a special FULLTEXT index that is used for text-searching purposes.
The implementation is the same on the server-side.
The only difference is that with CREATE INDEX syntax, you must specify a name for the index.
Whereas with ALTER TABLE, you may specify a name for the index, but you don't have to.
If you don't specify a name, the server generates a default name, as the name of the first column in the index, with a number suffix if necessary.
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