Now, if you execute the query again, you will find that the database engine uses the index for lookup: EXPLAIN SELECT * To create an index for the values in the phone column of the address table, you use the following statement: CREATE INDEX idx_address_phone To show the query plan, you use the EXPLAIN statement as follows: EXPLAIN SELECT * It is obvious that the database engine has to scan the whole address table to look for the address because there is no index available for the phone column. WHERE phone = '223664661973' Code language: JavaScript ( javascript ) The following query finds the address whose phone number is 223664661973: SELECT * FROM address We will use the address table from the sample database for the demonstration. PostgreSQL CREATE INDEX statement example To check if a query uses an index or not, you use the EXPLAIN statement. The NULLS FIRST is the default when DESC is specified and NULLS LAST is the default when DESC is not specified. If a column contains NULL, you can specify NULLS FIRST or NULLS LAST option. Finally, list one or more columns of the index.Third, specify the index method such as btree, hash, gist, spgist, gin, and brin.Second, specify the name of the table to which the index belongs.The index name should be meaningful and easy to remember. First, specify the index name after the CREATE INDEX clause.The following show the basic syntax of the CREATE INDEX statement: CREATE INDEX index_name ON table_name Ĭolumn_name , This is why indexes come into play.īy definition, an index is a separated data structure that speeds up the data retrieval on a table at the cost of additional writes and storage to maintain the index. Similar to a phonebook, the data stored in the table should be organized in a particular order to speed up various searches. This is called a sequential scan which you go over all entries until you find the one that you are looking for. If the names on the phone book were not ordered alphabetically, you would have to go through all pages and check every name until you find John Doe’s phone number. To find John Doe‘s phone number, you first look for the page where the last name is Doe, then look for the first name John, and finally, get his phone number. Assuming that the names on the phone book are in alphabetical order. Suppose you need to look up John Doe‘s phone number in a phone book. This sounds a bit overcomplicated for such a simple (and popular, I suppose) requirement.Summary: in this tutorial, you will learn about indexes and how to use the PostgreSQL CREATE INDEX statement to define a new index for a table. This, however, sounds like a really ugly hack.Īlternatively, it should be possible to use CREATE CONSTRAINT TRIGGER and manually check for case-insensitive uniqueness (of course a regular index would still be necessary). One possible workaround would be to create additional column with the same content as my_column, but upper case, updated via a trigger after each update/insert, then create a deferrable unique constraint on this artificial column. If deferrable constraint is not needed, it is as simple as creating unique index with function, e.g.: CREATE UNIQUE INDEX my_unique_index ON sample_table(UPPER(my_column)) ĭeferred constraint check requires creating the constraint explicitly, e.g.: ALTER TABLE sample_tableĪDD CONSTRAINT my_unique_constraint UNIQUE(my_column)Īnd unfortunately it is not possible to use arbitrary functions in unique constraint. Let's assume the following basic table: CREATE TABLE sample_table ( Is it possible in PostgreSQL to create a deferrable unique constraint on a character column, but case-insensitive?
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