Final answer:
The JOIN keyword is repeated for each table added beyond the first, and the ON keyword follows each JOIN to specify the join condition. For four tables, JOIN is used three times and ON is used three times.
Step-by-step explanation:
The keyword JOIN...ON is used to combine rows from two or more tables based on a related column between them. When joining multiple tables, the JOIN keyword is repeated for each new table you want to join. The ON keyword is then used immediately after each JOIN clause to specify the condition upon which the tables should be joined.
However, you do not need to repeat the JOIN...ON keywords four times when joining four tables. You need to use the JOIN keyword each time you introduce a new table, and the ON keyword should follow each JOIN to specify the join condition. So, if you are joining four tables, you will use the JOIN keyword three times after the first table (for each additional table), and similarly, you will have three ON clauses to specify each join condition.
In a join statement, the JOIN keyword is used to combine tables based on a common column between them, and the ON keyword is used to specify the condition for the join. You only need to specify the JOIN keyword once and the ON keyword once, regardless of the number of tables you are joining. The ON keyword is used to specify the column(s) on which the join is based, so each join condition would typically include the ON keyword followed by the join condition for that specific join. For example, if you are joining four tables, you would have three join conditions, each with the ON keyword followed by the specific condition for that join.