For loop with if else statement in SQL Server

Question

I'd like to create a loop and an IF Else statement in SQL Server to check a set of condition in each row of a table and do something if all conditions are met.

I'd like to do something like the example below in SQL Server:

For each row in table1:
   If (table1.dob is null
       and table1.name = table2.name
       and table1.surname=table2.surname){
       update table1
       set dob = table2.dob}
   Else {
      Do nothing
   End If
End loop

Can anyone help me please?

Thanks,

Eduardo

SQL is designed to tell database what to do, but not HOW to do it. SQL query engine will decide how to execute the query, so you don't need to write explicit imperative logic for your database. — twinmind
– twinmind, Commented Feb 6, 2018 at 1:12
Hi Daniel, in this example let's suppose I have only 2 tables: table 1 (name, surname, dob) and table 2 (name, surname, dob). Suppose I have many null values on table1.dob and no null values on table 2. Thanks — Eduardo Santiago
– Eduardo Santiago, Commented Feb 6, 2018 at 1:14
you can take the query from Tim's reply and change INNER JOIN to LEFT or RIGHT JOIN or OUTER JOIN to deal with nulls in the way you need — twinmind
– twinmind, Commented Feb 6, 2018 at 1:19

Tim Biegeleisen · Accepted Answer · 2018-02-06 01:08:35Z

5

You don't need loops for this, a standard update join should suffice:

UPDATE t1
SET dob = t2.dob
FROM table1 t1
INNER JOIN table2 t2
    ON t1.name = t2.name AND
       t1.surname = t2.surname
WHERE
    t1.dob IS NULL;

answered Feb 6, 2018 at 1:08

Tim Biegeleisen

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