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SQL return a default value if a row is not found [PostgreSQL]

The outer join will already take care of what you want.

As t1 is the "left table" of the join, all rows from t1 will be returned. Columns from the "right table" (t2 in your example) will then have a null value. So you only need to convert that null to a 0:

select t1.tag_id, coalesce(t2.cnt, 0)
from T1 t1 
    left join T2 t2 on t1.tag_Id=t2.tag_id 
and t1.place_id = 1;

SQLFiddle example:!12/ed7bf/1

Unrelated but:

Using count as a column name is a really bad idea, because it will require you to always enclose the column name in double quotes: t2."count" because it is a reserved word. Plus it doesn't really document the purpose of the column. You should find a better name for that.

Categories : SQL

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