SQL

Select

SELECT * FROM tab;
SELECT col1, col2 FROM tab;

Sort

SELECT * FROM tab ORDER BY col1 ASC;
SELECT * FROM tab ORDER BY col DESC;

Filter

By condition

SELECT * FROM tab WHERE col1 = 11;
SELECT * FROM tab WHERE col1 = 11 AND col2 > 5;

Check null

SELECT * FROM tab WHERE col1 IS NULL;
SELECT * FROM tab WHERE col1 IS NOT NULL;

Compare between columns

SELECT * FROM tab WHERE col1 > col2;

Add new column by calculation

SELECT col1, col2, col1/col2 AS new_col FROM tab;

Aggregate

Group sum

SELECT col1, SUM(col2) FROM tab GROUP BY col1;

Group average

SELECT col1, AVG(col2) FROM tab GROUP BY col1;

Multiple

SELECT col1, SUM(col2), MAX(col3) FROM tab GROUP BY col1;

Joining

Inner

SELECT * FROM tab1 INNER JOIN tab2 ON tab1.id = tab2.id;

Left

SELECT * FROM tab1 LEFT JOIN tab2 ON tab1.id = tab2.id;