


What's the Most Efficient Way to Extract a Date from a DATETIME Value in SQL Server?
Jan 13, 2025 am 08:00 AMEfficiently extract dates from date and time in SQL Server
Efficiently extracting dates from combined date and time values ??in SQL Server is critical for data manipulation tasks. In this case, the question is how to get the date from a datetime value like '2008-09-25 12:34:56'.
A variety of approaches have been proposed, including:
- CAST(FLOOR(CAST(CRETS AS FLOAT)) AS DATETIME)
This method converts the datetime value to a float, performs a floor operation to truncate the decimal part, and then converts the result back to datetime. Although very efficient, it was observed that this method is not the fastest in all situations.
- CONVERT(DATETIME, CONVERT(VARCHAR(10), CRETS, 120) , 120)
This method consists of converting the datetime value to a string of length 10 and then converting the string back to datetime if style 120 is specified (forcing date-only conversion).
- DATEADD(DAY, DATEDIFF(DAY, 0, CRETS), 0)
This method calculates the number of days between a datetime value and midnight, then adds that difference to midnight to get the date.
Performance Analysis
To determine the most efficient approach, we performed performance tests on large tables containing timestamps accurate to milliseconds. The following execution times were observed:
- Pure SELECT: 33803 ms
- Floor-cast: 33545 milliseconds
- String-convert: 33843 milliseconds
- DateAdd: 33440 milliseconds
Based on these results, DateAdd is slightly faster in certain test cases. Note that performance may vary based on data distribution, server configuration, and workload characteristics.
Therefore, when choosing the most efficient method to extract dates and times from SQL Server, it is recommended to evaluate various methods through performance testing based on specific data set and workload requirements.
The above is the detailed content of What's the Most Efficient Way to Extract a Date from a DATETIME Value in SQL Server?. For more information, please follow other related articles on the PHP Chinese website!

Hot AI Tools

Undress AI Tool
Undress images for free

Undresser.AI Undress
AI-powered app for creating realistic nude photos

AI Clothes Remover
Online AI tool for removing clothes from photos.

Clothoff.io
AI clothes remover

Video Face Swap
Swap faces in any video effortlessly with our completely free AI face swap tool!

Hot Article

Hot Tools

Notepad++7.3.1
Easy-to-use and free code editor

SublimeText3 Chinese version
Chinese version, very easy to use

Zend Studio 13.0.1
Powerful PHP integrated development environment

Dreamweaver CS6
Visual web development tools

SublimeText3 Mac version
God-level code editing software (SublimeText3)

Hot Topics

The default user name of MySQL is usually 'root', but the password varies according to the installation environment; in some Linux distributions, the root account may be authenticated by auth_socket plug-in and cannot log in with the password; when installing tools such as XAMPP or WAMP under Windows, root users usually have no password or use common passwords such as root, mysql, etc.; if you forget the password, you can reset it by stopping the MySQL service, starting in --skip-grant-tables mode, updating the mysql.user table to set a new password and restarting the service; note that the MySQL8.0 version requires additional authentication plug-ins.

GTID (Global Transaction Identifier) ??solves the complexity of replication and failover in MySQL databases by assigning a unique identity to each transaction. 1. It simplifies replication management, automatically handles log files and locations, allowing slave servers to request transactions based on the last executed GTID. 2. Ensure consistency across servers, ensure that each transaction is applied only once on each server, and avoid data inconsistency. 3. Improve troubleshooting efficiency. GTID includes server UUID and serial number, which is convenient for tracking transaction flow and accurately locate problems. These three core advantages make MySQL replication more robust and easy to manage, significantly improving system reliability and data integrity.

There are three ways to modify or reset MySQLroot user password: 1. Use the ALTERUSER command to modify existing passwords, and execute the corresponding statement after logging in; 2. If you forget your password, you need to stop the service and start it in --skip-grant-tables mode before modifying; 3. The mysqladmin command can be used to modify it directly by modifying it. Each method is suitable for different scenarios and the operation sequence must not be messed up. After the modification is completed, verification must be made and permission protection must be paid attention to.

MySQL main library failover mainly includes four steps. 1. Fault detection: Regularly check the main library process, connection status and simple query to determine whether it is downtime, set up a retry mechanism to avoid misjudgment, and can use tools such as MHA, Orchestrator or Keepalived to assist in detection; 2. Select the new main library: select the most suitable slave library to replace it according to the data synchronization progress (Seconds_Behind_Master), binlog data integrity, network delay and load conditions, and perform data compensation or manual intervention if necessary; 3. Switch topology: Point other slave libraries to the new master library, execute RESETMASTER or enable GTID, update the VIP, DNS or proxy configuration to

The steps to connect to the MySQL database are as follows: 1. Use the basic command format mysql-u username-p-h host address to connect, enter the username and password to log in; 2. If you need to directly enter the specified database, you can add the database name after the command, such as mysql-uroot-pmyproject; 3. If the port is not the default 3306, you need to add the -P parameter to specify the port number, such as mysql-uroot-p-h192.168.1.100-P3307; In addition, if you encounter a password error, you can re-enter it. If the connection fails, check the network, firewall or permission settings. If the client is missing, you can install mysql-client on Linux through the package manager. Master these commands

Toalteralargeproductiontablewithoutlonglocks,useonlineDDLtechniques.1)IdentifyifyourALTERoperationisfast(e.g.,adding/droppingcolumns,modifyingNULL/NOTNULL)orslow(e.g.,changingdatatypes,reorderingcolumns,addingindexesonlargedata).2)Usedatabase-specifi

InnoDB implements repeatable reads through MVCC and gap lock. MVCC realizes consistent reading through snapshots, and the transaction query results remain unchanged after multiple transactions; gap lock prevents other transactions from inserting data and avoids phantom reading. For example, transaction A first query gets a value of 100, transaction B is modified to 200 and submitted, A is still 100 in query again; and when performing scope query, gap lock prevents other transactions from inserting records. In addition, non-unique index scans may add gap locks by default, and primary key or unique index equivalent queries may not be added, and gap locks can be cancelled by reducing isolation levels or explicit lock control.

The function of InnoDBBufferPool is to improve MySQL read and write performance. It reduces disk I/O operations by cacheing frequently accessed data and indexes into memory, thereby speeding up query speed and optimizing write operations; 1. The larger the BufferPool, the more data is cached, and the higher the hit rate, which directly affects database performance; 2. It not only caches data pages, but also caches index structures such as B-tree nodes to speed up searches; 3. Supports cache "dirty pages", delays writing to disk, reduces I/O and improves write performance; 4. It is recommended to set it to 50%~80% of physical memory during configuration to avoid triggering swap; 5. It can be dynamically resized through innodb_buffer_pool_size, without restarting the instance.
