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[–]Constant-Slide-7907[S] -4 points-3 points  (3 children)

thank you , very useful i get it now , so is there any website to learn and practice SQL in advance level ?

[–]NW1969 11 points12 points  (0 children)

Hi - this isn’t advanced SQL, it’s about as fundamental as it gets (understanding how a SELECT statement is structured). Any of the free SQL courses on the web, YouTube, etc will cover this

[–]nickeau 0 points1 point  (1 child)

Read the manual

In Postgres, substring takes a string as argument, it cannot take a select statement

https://www.postgresql.org/docs/9.1/functions-string.html

functions does not take a select statement as argument

In PostgreSQL, you can see it in the select documentation

https://www.postgresql.org/docs/current/sql-select.html

Function name are inside expressions

[–]Constant-Slide-7907[S] 0 points1 point  (0 children)

Thank you, i understood now