MySQL - UNLOCK INSTANCE Statement

MySQL UNLOCK INSTANCE Statement

You can create an instance level backup lock using the MySQL LOCK INSTANCE FOR BACKUP Statement. This lock allows manipulations on the data during an online backup. This prevents operations that effect the consistency of the transactions.

If the current session is terminated all the backup instance locks will be released. You can also backup lock instance using the UNLOCK INSTANCE Statement.

Syntax

Following is the syntax of the MySQL UNLOCK INSTANCE statement −

UNLOCK INSTANCE

Example

Suppose we have created a table that contains the sales details along with the contact details of the customers as shown below −

CREATE TABLE SALES_DETAILS (
   ID INT,
   ProductName VARCHAR(255),
   CustomerName VARCHAR(255),
   DispatchDate date,
   DeliveryTime time,
   Price INT,
   Location VARCHAR(255),
   CustomerAge INT,
   CustomrtPhone BIGINT,
   DispatchAddress VARCHAR(255),
   Email VARCHAR(50)
);

Now, let’s insert 2 records into the above created table using the INSERT statement as −

Insert into SALES_DETAILS values
(1, 'Key-Board', 'Raja', DATE('2019-09-01'), TIME('11:00:00'), 7000, 
'Hyderabad', 25, '9000012345', 'Hyderabad – Madhapur', 
'pujasharma@gmail.com'),
(2, 'Mobile', 'Vanaja', DATE('2019-03-01'), TIME('10:10:52'), 9000, 
'Chennai', 30, '9000012365', 'Chennai- TNagar', 
'vanajarani@gmail.com');

If we want another table with just the contact details of the customer create a table as −

CREATE TABLE CustContactDetails (
   ID INT,
   Name VARCHAR(255),
   Age INT,
   Phone BIGINT,
   Address VARCHAR(255),
   Email VARCHAR(50)
);

Following query insets records into the CustContactDetails table using the INSERT INTO SELECT statement. Here, we are trying to insert records from the SALES_DETAILS table to CustContactDetails table −

INSERT INTO CustContactDetails (ID, Name, Age, Phone, Address, Email)
SELECT
ID, CustomerName, CustomerAge, CustomrtPhone, DispatchAddress, Email
FROM SALES_DETAILS 
WHERE ID = 1 AND CustomerName = 'Raja';

Let us insert another record −

INSERT INTO CustContactDetails (ID, Name, Age, Phone, Address, Email)
SELECT
ID, CustomerName, CustomerAge, CustomrtPhone, DispatchAddress, Email
FROM SALES_DETAILS
WHERE ID = 2 AND CustomerName = 'Vanaja';

You can verify the contents of the CustContactDetails table as shown below −

SELECT * FROM CustContactDetails;

Output

Following is the output of the above program −

Following set of queries locks the instance flushes the above created tables and unlocks the instance. −

LOCK INSTANCE FOR BACKUP;

FLUSH TABLES emp, custcontactdetails WITH READ LOCK;

UNLOCK TABLES;

UNLOCK INSTANCE;