SQL INNER JOIN Tutorial ?? How Does a JOIN work? ?? INNER JOIN and NULLs

#sql #mysql #data

A join clause in SQL combines columns from one or more tables into a new table. ANSI-standard SQL specifies five types of JOIN: INNER, LEFT OUTER, RIGHT OUTER, FULL OUTER and CROSS.

In this video we will look into INNER JOIN ??

00:00 How does inner join work in SQL?
01:00 SQL JOIN syntax
02:25 SQL ambigous column error
03:22 Inner Join Result in SQL
03:54 NULL in SQL joins
04:54 Using alias in SQL joins
06:16 Perfect inner join

? What is an INNER JOIN?

An inner join requires each row in the two joined tables to have matching column values, and is a commonly used join operation in applications but should not be assumed to be the best choice in all situations. Inner join creates a new result table by combining column values of two tables (A and B) based upon the join-predicate. The query compares each row of A with each row of B to find all pairs of rows that satisfy the join-predicate. When the join-predicate is satisfied by matching non-NULL values, column values for each matched pair of rows of A and B are combined into a result row.

? INNER JOIN and NULL

Data analyst should take special care when joining tables on columns that can contain NULL values, since NULL will never match any other value (not even NULL itself), unless the join condition explicitly uses a combination predicate that first checks that the joins columns are NOT NULL before applying the remaining predicate condition(s).