问题
When trying to use the WHERE NOT EXISTS clause to prevent adding a row with a duplicate value in the column age, I get the error syntax error at or near "WHERE".
Why did it throw a syntax error? I'm using Postgresql 9.1.
SQL
INSERT INTO live.users ("website", "age")
values ('abc', '123')
WHERE NOT EXISTS (SELECT age FROM live.users WHERE age = 123);
Error
ERROR: syntax error at or near "WHERE"
LINE 6: WHERE NOT EXISTS (SELECT age FROM live.users W...
回答1:
Do instead:
INSERT INTO live.users ("website", "age")
SELECT 'abc', 123
WHERE NOT EXISTS (SELECT age FROM live.users WHERE age = 123);
回答2:
INSERT INTO live.users ("website", "age")
select 'abc', '123'
WHERE NOT EXISTS (SELECT age FROM live.users WHERE age = 123);
回答3:
I encountered some issues in using WHERE field NOT EXISTS in PLPGSQL. Instead what worked well was WHERE field NOT IN, I received no function errors after using that.
回答4:
I see you asked for v9.1 but it's been 4 yrs since and now, starting from PostgreSQL v9.5 - INSERT gives you ON CONFLICT … DO NOTHING option:
INSERT INTO live.users("website", "age") VALUES('abc', '123') ON CONFLICT ("age") DO NOTHING
Worth noting this requires respective constraint set up on the target table - but in most cases, I imagine you would have it anyway. Otherwise you'll get:
ERROR: there is no unique or exclusion constraint matching the ON CONFLICT specification
来源：https://stackoverflow.com/questions/15840922/where-not-exists-in-postgresql-gives-syntax-error