SQL Query to Find Record with Id Not in Another Table

SQL query to find record with ID not in another table

Try this

SELECT ID, Name 
FROM   Table1 
WHERE  ID NOT IN (SELECT ID FROM Table2)

SQL to find record with a value in one table but not another table

Assuming your IDs do not change in either table so that ID 100 in Address always points to ID 100 in Address_Backup:

  SELECT * 
    FROM Address_Backup
     WHERE ID NOT IN (SELECT ID FROM Address) AND Code = 'OTHER'

using NOT EXISTS

 SELECT * 
  FROM Address_Backup AS B
  WHERE NOT EXISTS (SELECT 1 FROM Address WHERE ID = B.ID) AND Code = 'OTHER'

How to select all records from one table that do not exist in another table?

SELECT t1.name
FROM table1 t1
LEFT JOIN table2 t2 ON t2.name = t1.name
WHERE t2.name IS NULL

Q: What is happening here?

A: Conceptually, we select all rows from table1 and for each row we attempt to find a row in table2 with the same value for the name column. If there is no such row, we just leave the table2 portion of our result empty for that row. Then we constrain our selection by picking only those rows in the result where the matching row does not exist. Finally, We ignore all fields from our result except for the name column (the one we are sure that exists, from table1).

While it may not be the most performant method possible in all cases, it should work in basically every database engine ever that attempts to implement ANSI 92 SQL

Find ID which doesn't exist from another table

You can try below.

Using EXCEPT

select OrderID from reference_OrderTable
EXCEPT
select OrderID from OrderTable

using join

select r.OrderID from reference_OrderTable r 
LEFT JOIN OrderTable o ON o.OrderID = r.OrderID
WHERE o.OrderID IS NULL

using sub queries

select OrderID from reference_OrderTable
where OrderID NOT IN (select OrderID from OrderTable)

Optimizing sql query: check for all rows in table B if any rows in table C reference the same row in table A

Simply move the EXISTS clause into your SELECT clause.

SELECT
  b.id,
  EXISTS (SELECT null FROM c WHERE c.a_id = b.a_id) AS c_exists
FROM b;

The same with an IN clause, which I prefer for being even a tad simpler:

SELECT
  id,
  a_id IN (SELECT c.a_id FROM c) AS c_exists
FROM b;

Is there a standard method to have unique values in SQL table per parent record

You can create a UNIQUE constraint, as in:

alter table my_table
add constraint uq1 unique (ListID, ItemID);

How to select rows with no matching entry in another table?

Here's a simple query:

SELECT t1.ID
FROM Table1 t1
    LEFT JOIN Table2 t2 ON t1.ID = t2.ID
WHERE t2.ID IS NULL

The key points are:

1. LEFT JOIN is used; this will return ALL rows from Table1, regardless of whether or not there is a matching row in Table2.

2. The WHERE t2.ID IS NULL clause; this will restrict the results returned to only those rows where the ID returned from Table2 is null - in other words there is NO record in Table2 for that particular ID from Table1. Table2.ID will be returned as NULL for all records from Table1 where the ID is not matched in Table2.

How to select everything NOT in a table from another table in Snowflake?

The MINUS way:

Well not a CTE at all, but given your rows are "all the same" you could do a MINUS:

SELECT id, value, value2 FROM table1
MINUS 
SELECT id, value, value2 FROM table2;

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