How to find record with id not in another table?
FROM ( (SELECT id FROM table1) EXCEPT (SELECT id FROM table2) ) t1_not_in_t2 JOIN table1 ON t1_not_in_t2.id=table1.id; Keeping in mind the points made in @John Woo’s comment/link above, this is how I typically would handle it:
How to select all rows from one table?
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.
How to select all records from one table that does not exist?
This is the strategy: you create two implicit temporary tables and make a union of them. The first temporary table comes from a selection of all the rows of the first original table the fields of which you wanna control that are NOT present in the second original table.
How to select rows with no matching entry?
Table 1 has a column that you want to add the foreign key constraint to, but the values in the foreign_key_id_column don’t all match up with an id in table 2. The initial select lists the id s from table1.
Why are records in one table not present in another?
The objective is to fetch all records in one table that are not present in another table. The most common code I’ve seen at client sites includes the use of NOT IN, because this keyword is included in most programming languages and programmers tend to use this technique when writing stored procedures in the database too.
Do you need an index for both tables?
You’ll need an index for both tables. If you look at the query plan it will look something like this and you can confirm your new index is actually being used. Note this is for SQL Server but should be similar for MySQL.
How to find records from two table in SQL?
With large tables the database will most likely choose to scan both tables. You should create indexes both Phone_Book and Call containing the phone_number. If performance is becoming an issue try an lean index like this, with only the phone number: The fewer fields the better since it will have to load it entirely.