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memorize.ai

memorize.ai (lvl 286)

Section 1

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Left Join

Front

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Last updated

6 years ago

Date created

Mar 1, 2020

Cards (5)

Section 1

(5 cards)

Left Join

Front

returns all rows from the left table (table1), with the matching rows in the right table (table2). The result is NULL in the right side when there is no match. SELECT column_name(s) FROM table1 "" JOIN table2 ON table1.column_name=table2.column_name;

Back

Full join

Front

Return all rows when there is a match in ONE of the tables

Back

What is the purpose of join tables?

Front

Join tables are good for when you are not sure if there is a value for the field you are searching for but know that in one table there is more values for that field. The main differentiator is that it will bring up the NULL values. You are selecting all records from one table that mets one condition from the other table. The important thing to note is that the first database is selecting all records from table 1, along with records that match in table 2 .

Back

Inner Join

Front

will show all the rows selected from both tables when the condition satisfies, as in a key in one table is the same exact as the other key.

Back

Right join

Front

returns all the rows from the right table with the match rows in the left table. The result is null in the right side where there is no match.

Back