防止在MySql中插入匹配的行

Question

I have a table in MySql Database. I would like to prevent inserting matching rows in MySql. Like I have 4 columns in a table. I would not like to insert any row which has matching values of these 4 columns. I am trying to show that below

My table
----------
 product_name| product_sku |product_quantity| product_price
----------
 Computer    | comp_007    | 5              | 500

I would like to prevent to insert same row again. How can I do that using MySql Query ??

UPDATE

I would not like to insert again

---

 Computer    | comp_007    | 5              | 500

But I would like to insert below rows

---

 mouse       | comp_007    | 5               | 500

---

 Computer    | comp_008    | 5               | 500

---

 Computer    | comp_007    | 50              | 500

---

 Computer    | comp_007    | 5               | 100

---

 mouse       | mou_007     | 5               | 500

Answer 1

Create a combined unique key / composite key on the columns in question:

ALTER TABLE `table` ADD UNIQUE (
`product_name` ,
`product_sku` ,
`product_quantity`,
`product_price`
);

Any attempts to insert duplicate rows will result in a MySQL error.

Answer 2

If possible you should add a Unique Key to your columns:

ALTER TABLE `table_name` 
ADD UNIQUE INDEX `ix_name` (`product_name`, `product_sku`, `product_quantity`, `product_price`);

and then use INSERT IGNORE :

INSERT IGNORE INTO table_name (product_name, product_sku, product_quantity, product_price) VALUES (value1, value2, value3, value4);

If the record is unique MYSQL inserts it as usual, if the record is a duplicate then the IGNORE keyword discards the insert without generating an error.

SQLfiddle

Answer 3

The simplest way would be to make your columns unique. On undesired inserts, your MySQL driver should throw an exception then, which you can handle.

From a domain logic point of view, this is a bad practice, since exceptions should never handle expected behaviour. By the way, your DB table could use a primary key.

So, to have a better solution, your approach could be: - Define a unique field (the SKU seems suitable); think about using this as the primary key as well - With MySQL, use a REPLACE statement:

REPLACE INTO your_tablename
SET product_name='the name'
-- and so on for other columns
WHERE product_sku = 'whatever_sku';

REPLACE does the Job of trying to INSERT, and doing an UPDATE instead if the PK exists.