Regular expression: Postgres SQL query is returning all records available in the table

Question

The below Postgres SQL query is returning all records available in the table. Can someone give explanation for this? . Also please let me know what * represents in case of postgres regular expression.

Employee table contains :

name
Chennai
Delhi
Hydrabad
NewYark
ABC

select * from employee where name ~ 'Z*'

Answer 1

This is the correct query for finding name starting with 'Z' :

SELECT record FROM myrecords WHERE name ~ '^Z';

in your query :

select * from employee where name ~ 'Z*'

the meaning is where the name matches ZERO or MORE sequences of character "Z", hence returning all records.

• * in the matching criteria means ZERO or MORE occurences.

• * along with tilda means case insensitive match ie ~* 'Z' will match both "z" and "Z"

For more have a look here :

http://oreilly.com/pub/a/databases/2006/02/02/postgresq_regexes.html?page=1

Answer 2

The * quantifier means zero or more . Since every name contains at least zero Z characters, every row is returned.

You don't need to use a regex to find strings starting with a character, you can just use LIKE :

SELECT record FROM myrecords WHERE name LIKE 'Z%';

If you want names starting with Z using a regex , try this:

SELECT record FROM myrecords WHERE name ~ '^Z';

If you want names containing at least one Z, try one of these:

SELECT record FROM myrecords WHERE name LIKE '%Z%';
SELECT record FROM myrecords WHERE name ~ 'Z';