CODEWITHSUNDEEP
sqloracle-databaseif-statementexists
Matt
Matt

Reputation: 2843

Oracle sql return true if exists question

How do I check if a particular element exists in a table - how can I return true or false?

I have a table that has

Verbally, I want to do this: If a particular user_id exists in the user_id column, then return true -- otherwise return false.

Upvotes: 24

Views: 121041

Answers (6)

Adrian Sanchez
Adrian Sanchez

Reputation: 191

I use something like this using Oracle:

SELECT CASE WHEN EXISTS (
    { MY SELECT QUERY HERE }
) THEN 1 ELSE 0 END AS result
FROM DUAL;

For example:

SELECT CASE WHEN EXISTS (
    SELECT 1
    FROM mytable t
    WHERE t.column1 = 1234 AND t.column2 = 4444
) THEN 1 ELSE 0 END AS result
FROM DUAL;

Upvotes: 0

Johnbabu Koppolu
Johnbabu Koppolu

Reputation: 3252

Oracle RDBMS does not have boolean data type, you can only use boolean variables in PL/SQL.

If you simply want to return strings 'TRUE' and 'FALSE' you can do this..

SELECT 'TRUE'  FROM DUAL WHERE EXISTS (SELECT 'x' FROM  table WHERE user_id = 'id')
UNION
SELECT 'FALSE' FROM DUAL WHERE NOT EXISTS (SELECT 'x' FROM  table WHERE user_id = 'id')

I like @DCookie's query though.

Upvotes: 9

mk.chan
mk.chan

Reputation: 39

Or you could do this:

select decode(max(USER_ID), null, 'FALSE', 'TRUE') BOOL_VAL
from USER_TABLE where USER_ID = [some USER_ID here]

Upvotes: 3

grokster
grokster

Reputation: 6297

select count(*) from table where userid = :userid and rownum <= 1); -- If exists then 1 else 0

Upvotes: 5

Tony Andrews
Tony Andrews

Reputation: 132690

In PL/SQL you can do this:

function user_exists (p_user_id users.user_id%type) return boolean
is
  l_count integer;
begin
  select count(*)
  into   l_count
  from   users
  where  user_id = p_user_id;

  return (l_count > 0);
end;

This would then be used in calling PL/SQL like this:

if user_exists('john') then
  dbms_output.put_Line('John exists');
end if;

NOTE: I used count(*) in the query in the knowledge that this will only return 1 or 0 in the case of a primary key search. If there could be more than one row then I would add "and rownum = 1" to the query to prevent unnecessarily counting many records just to find out if any exists:

function user_has_messages (p_user_id users.user_id%type) return boolean
is
  l_count integer;
begin
  select count(*)
  into   l_count
  from   messages
  where  user_id = p_user_id
  AND ROWNUM = 1;

  return (l_count > 0);
end;

Upvotes: 11

DCookie
DCookie

Reputation: 43533

There is no Boolean type in Oracle SQL. You will need to return a 1 or 0, or some such and act accordingly:

SELECT CASE WHEN MAX(user_id) IS NULL THEN 'NO' ELSE 'YES' END User_exists
  FROM user_id_table
 WHERE user_id = 'some_user';

Upvotes: 54

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