which query is better and efficient - mysql

Question

I came across writing the query in differnt ways like shown below Type-I

SELECT JS.JobseekerID
         , JS.FirstName
         , JS.LastNam         


        

Answer 1

For the two queries you mentioned (each with only inner joins) any modern database's query optimizer should produce exactly the same query plan, and thus the same performance.

For MySQL, if you prefix the query with EXPLAIN, it will spit out information about the query plan (instead of running the query). If the information from both queries is the same, them the query plan is the same, and the performance will be identical. From the MySQL Reference Manual:

EXPLAIN returns a row of information for each table used in the SELECT statement. The tables are listed in the output in the order that MySQL would read them while processing the query. MySQL resolves all joins using a nested-loop join method. This means that MySQL reads a row from the first table, and then finds a matching row in the second table, the third table, and so on. When all tables are processed, MySQL outputs the selected columns and backtracks through the table list until a table is found for which there are more matching rows. The next row is read from this table and the process continues with the next table.

When the EXTENDED keyword is used, EXPLAIN produces extra information that can be viewed by issuing a SHOW WARNINGS statement following the EXPLAIN statement. This information displays how the optimizer qualifies table and column names in the SELECT statement, what the SELECT looks like after the application of rewriting and optimization rules, and possibly other notes about the optimization process.

As to which syntax is better? That's up to you, but once you move beyond inner joins to outer joins, you'll need to use the newer syntax, since there's no standard for describing outer joins using the older implicit join syntax.