Programmer Think

👨‍🎓 Blogger introduction: IT Bond, a Jianghu person jeames007，10 year DBA hands-on background China DBA union(ACDU)Member, currently engaged in DBA And program programming SQL is almost a necessary skill for the production and research position of Internet companies, but if you only know SQL, you can't do anything. 1. If you are a da ...

Introduction to LEFT SEMI JOIN The main use scenario of SEMI JOIN (equivalent to LEFT SEMI JOIN) is to solve EXISTS IN. LEFT SEMI JOIN is a more efficient implementation of IN/EXISTS sub query. Although LEFT SEMI JOIN contains LEFT, its implementation effect is equivalent to INNER JOIN, but the JOIN result only takes the columns in the orig ...

Continuous check-in and receive gold coins describe User behavior log table tb_user_log (uid - user ID, artistic_id - article ID, in_time - entry time, out_time - departure time, sign_in - check in or not) Scenario Logic Description: artical_id - article ID represents the ID of the article the user browses. In special cases, it is artistic ...

Subquery (Continued) Comparison operator (Continued) Demonstration: how to use comparison operators in multivalued subqueries Example A: query all orders with product category No. 1 and return all field data of the order Subquery select * from sales.orders where orderid in ( select orderid from sales.orderdetails ...

1. Spark SQL architecture design The development of big data is realized by using SQL directly. It supports both DSL and SQL syntax style. At present, in the whole architecture design of spark, all spark modules, such as SQL, SparkML, sparkGrahpx and structured streaming, run on the catalyst optimization & tungsten execution module, The fo ...

[Abstract] as an OLAP database, Clickhouse has very limited support for transactions. This paper mainly introduces how to update and delete Clickhouse data through replacing mergetree. As an OLAP database, Clickhouse has very limited support for transactions. Clickhouse provides the movement operation (through the ALTER TABLE statement) to UPD ...

Database is very important. Without backup, data loss can only run away. So make a backup! 1, Tool introduction mysql dump is a logical backup tool that comes with mysql. Its backup principle is to connect to mysql database through protocol, query the data to be backed up, and convert the queried data into corresponding insert statements. ...

SQLmap usage Usage: python sqlmap.py [option] Options: -h, --help Display basic help information and exit -hh Show advanced help and exit --version Display program version information and exit -v VERBOSE Output information detail level: 0-6((default = 1) Objectives: Provide a ...

Application and syntax rules of MySQL sub query: Let's first introduce an example: compare whose salary is higher than Abel in the salary table Method 1 (carried out in two steps), the reference code is as follows: SELECT salary FROM employees WHERE last_name = 'Abel'; SELECT last_name,salary FROM employees WHERE salary > 11000; Method ...

Introduction: the method of making some simulated data summary Making data can be used on some strange occasions. Generally, we have data before we have data-based applications, but conversely, if the application gets another scenario, there is no way to demonstrate without data function. Generally, more real data can be applied to function ...