如何将Sql转换为Oracle查询

Question

I have sql query like :-

SELECT CASE WHEN (NOT EXISTS(SELECT NULL 
FROM [Customers] AS t0
WHERE NOT (LEN(t0.[ContactName]) > 0)
)) THEN 1 ELSE 0 END AS [value]

Please let me know how I can convert to oracle query? Thanks in advance. Joon

Answer 1

In Oracle, an empty string and NULL are identical so LENGTH( NULL ) and LENGTH( '' ) will both give NULL and not 0 .

So your query would be:

SELECT CASE
       WHEN NOT EXISTS(
         SELECT 1 
         FROM   Customers
         WHERE  ContactName IS NULL
       )
       THEN 1
       ELSE 0
       END AS value
FROM   DUAL

Update :

What if I want to find out all records has length of contactname bigger than 3

SELECT CASE
       WHEN NOT EXISTS(
         SELECT 1 
         FROM   Customers
         WHERE  LENGTH( ContactName ) <= 2
         OR     ContactName IS NULL
       )
       THEN 1
       ELSE 0
       END AS value
FROM   DUAL

or

SELECT CASE
       WHEN NOT EXISTS(
         SELECT 1 
         FROM   Customers
         WHERE  COALESCE( LENGTH( ContactName ), 0 ) <= 2
       )
       THEN 1
       ELSE 0
       END AS value
FROM   DUAL

Note: to use an index you will need a function-based index on LENGTH( ContactName ) or COALESCE( LENGTH( ContactName ), 0 ) for the respective examples.

Answer 2

If your SQL checks "if there exists an empty contact name in the customers table" then you can use the oracle queries below.

SELECT DECODE(cnt, 0, 0, 1)
  FROM (SELECT COUNT(1) cnt
          FROM customers
         WHERE NOT NVL(LENGTH(contact_name), 0) > 0);

or

SELECT DECODE(cnt, 0, 0, 1)
  FROM (SELECT COUNT(1) cnt
          FROM customers
         WHERE contact_name IS NULL);

Answer 3

to avoid null error use nvl function:

SELECT
  CASE
    WHEN (NOT EXISTS
      (SELECT NULL FROM Customers t0 WHERE NOT NVL(LENGTH(t0.ContactName),0) > 0
      ))
    THEN 1
    ELSE 0
  END val
FROM DUAL;

Answer 4

I got it like that:

SELECT CASE WHEN (NOT EXISTS(SELECT NULL FROM Customers  t0 WHERE NOT 
    LENGTH(t0.ContactName) > 0)) THEN 1 ELSE 0 END val
FROM DUAL

thanks all