正则表达式：Postgres SQL查询返回表中所有可用的记录

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';