MySQL Programming Interview Questions and Answers

1 :: How To Drop an Existing View in MySQL?

If you have an existing view, and you don't want it anymore, you can delete it by using the "DROP VIEW viewName" statement as shown in the following script:

mysql> DROP VIEW faqComment;
Query OK, 0 rows affected (0.00 sec)

mysql> SELECT * FROM faqComment;
ERROR 1146 (42S02): Table 'ggl.faqcomment' doesn't exist

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2 :: How To Create a New View in MySQL?

You can create a new view based on one or more existing tables by using the "CREATE VIEW viewName AS selectStatement" statement as shown in the following script:

mysql> CREATE TABLE comment (faqID INTEGER,
message VARCHAR(256));
Query OK, 0 rows affected (0.45 sec)

mysql> INSERT INTO comment VALUES (1, 'I like it');
Query OK, 1 row affected (0.00 sec)

mysql> CREATE VIEW faqComment AS SELECT f.id, f.title,
f.description, c.message FROM faq f, comment c
WHERE f.id = c.faqID;
Query OK, 0 rows affected (0.06 sec)

mysql> SELECT * FROM faqComment;

+----+-------------+-------------------------+-----------+

| id | title       | description             | message   |

+----+-------------+-------------------------+-----------+

|  1 | Learn MySQL | Visit www.GlobalGuideLine.com | I like it |

+----+-------------+-------------------------+-----------+

1 row in set (0.07 sec)

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3 :: How To Drop an Existing Index in MySQL?

If you don't need an existing index any more, you should delete it with the "DROP INDEX indexName ON tableName" statement. Here is an example SQL script:

mysql> DROP INDEX tip_subject ON tip;
Query OK, 0 rows affected (0.13 sec)
Records: 0 Duplicates: 0 Warnings: 0

mysql> SHOW INDEX FROM TIP;

+------------+-------------+--------------+-------------+...

| Non_unique | Key_name    | Seq_in_index | Column_name |...

+------------+-------------+--------------+-------------+...

|          0 | PRIMARY     |            1 | id          |...

+------------+-------------+--------------+-------------+...

1 row in set (0.00 sec)

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4 :: How To Get a List of Indexes of an Existing Table?

If you want to see the index you have just created for an existing table, you can use the "SHOW INDEX FROM tableName" command to get a list of all indexes in a given table. The tutorial script below shows you a nice example:

mysql> SHOW INDEX FROM TIP;

+------------+-------------+--------------+-------------+...

| Non_unique | Key_name    | Seq_in_index | Column_name |...

+------------+-------------+--------------+-------------+...

|          0 | PRIMARY     |            1 | id          |...

|          1 | tip_subject |            1 | subject     |...

+------------+-------------+--------------+-------------+...

2 rows in set (0.03 sec)

It's interesting to see that there is a default index for the primary key column.

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5 :: How To Create a Table Index in MySQL?

If you have a table with a lots of rows, and you know that one of the columns will be used often as a search criteria, you can add an index for that column to improve the search performance. To add an index, you can use the "CREATE INDEX" statement as shown in the following script:

mysql> CREATE TABLE tip (id INTEGER PRIMARY KEY,
subject VARCHAR(80) NOT NULL,
description VARCHAR(256) NOT NULL,
create_date DATE NULL);
Query OK, 0 rows affected (0.08 sec)

mysql> CREATE INDEX tip_subject ON tip(subject);
Query OK, 0 rows affected (0.19 sec)
Records: 0 Duplicates: 0 Warnings: 0

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