MySQL query from multiple tables? - php

Question

I have two tables say named table_1 and table_2. The schema is somewhat as follows.
table_1
+----+--------+-----+------------+
| id | reg_no | ... | table_2_id |
+----+--------+-----+------------+
table_2
+----+-----+
| id | ... |
+----+-----+
The column table_2_id in table_1 refers to the column id in table_2. Now, I have to get the table_2_id for a specific reg_no and then use that table_2_id to get data from table_2.
I currently do it as follows and it works.
$stmt = $this->conn->prepare("SELECT table_2_id from table_1 WHERE reg_no = ?");
$stmt->bind_param("s", $reg_no);
$stmt->execute();
$stmt->bind_result($table_2_id);
$stmt->fetch();
$stmt->close();
$stmt = $this->conn->prepare("SELECT * from table_1 WHERE id = ?");
$stmt->bind_param("i", $table_2_id);
$stmt->execute();
...
Is this the correct way to do it? Is there some other more efficient query to perform this task?

Answer 1

The query using join
SELECT t2.*
FROM table_1 t1
JOIN table_2 t2 ON t1.table_2_id = t2.id
WHERE t2.t1reg_no = ?

Answer 2

It should be more efficient to do this with one query like this:
SELECT table_2.*
FROM table_1 LEFT JOIN table_2 ON table_1.table_2_id=table_2.id
WHERE table_1.reg_no = ?
table_1 LEFT JOIN table_2 ON table_1.table_2_id=table_2.id will join table_1 and table_2.
More specifically it will create a table which will have all columns from both table_1 and table_2
and then it will put in it all rows from table_1. Also when there is a row in table_2 with id same as the
table_2_id it will also fill the tables_2's columns.
The above action will be limited to only those rows where table_1.reg_no = ?
Finally with SELECT table_2.* we get only the columns from the table_2 as in your example.

Answer 3

Try
SELECT T2.* FROM table_2 T2
LEFT JOIN table_1 T1 ON T1.table_2_id = T2.id
WHERE T1.reg_no = ?;
Example
table_1
id reg_no table_2_id
1 001 1
2 002 2
3 003 4
4 004 7
5 005 8
table_2
id column_test
1 A
2 B
3 C
4 D
5 E
6 F
7 G
Query
SELECT T2.* FROM table_2 T2
LEFT JOIN table_1 T1 ON T1.table_2_id = T2.id
WHERE T1.reg_no = 003;
Output
id column_test
4 D