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Introduction to Spark SQL Spark SQL is one of the most complex components in spark technology. It provides the function of operating structured data in Spark Program, that is, SQL query. Specifically, spark SQL has the following three important features: 1.Spark SQL supports reading of multiple structured data formats, such as JSON,Parquet ...

This article is about Learning Guide for Big Data Specialists from Zero (Full Upgrade) ClickHouse: Partial supplement. 0 Explain View Execution Plan To view the execution plan of an sql statement before Clickhouse version 20.6, you need to set the log level to trace to be visible and can only actually execute sql and view it in the executio ...

1 View The difference between a view and a table: "Is the actual data saved?""Views are not tables. Views are virtual tables. Views depend on tables." 1.1 Create View CREATE VIEW <View Name>(<Column Name 1>,<Column Name 2>,...) AS <SELECT Sentence> -- Create views based on multiple tables wit ...

High performance server, network theoretical knowledge and operating system High performance server Improve server performance 1. I/O model Blocking IO (not appropriate) Program blocking and read / write function when there is no data to read, the program blocks until the data is read successfully Blocking process: the time period whe ...

1 operator 1.1 arithmetic operators meaningoperatoraddition+subtraction-multiplication*division/ 1.2 comparison operators operatormeaning=Equal to<>And ~ are not equal>=Greater than or equal to>greater than<=Less than or equal to<less than 2 exercise part 1 - query 2.1 writing the product table The SQL code is as foll ...

1. sql Title Brushing There are two main purposes to do this topic, preparing for the interview and understanding the business logic and thinking style of the data analyst in practice. Most of the data analysts are biased toward the business side, with the indicators increasing or decreasing, how to analyze, from which angles to analyze, c ...

Build table 1. Table building syntax Table creation belongs to DDL statements, including create, drop and alter create table Table name (field name 1 data type, field name 2 data type, field name 3 data type,) 2. Data type varchar: variable length string, which is slow and saves space char: fixed length string. Regardless of the actual d ...

catalogue 1, Advantages 2, Create databases and tables 3, Basic usage syntax (addition, deletion, modification and query)   1. Increase 2. Delete 3. Change 4. Check 1, Advantages Simple: compared with other large databases, MySQL is a relatively simple database system, which is easier to use than XiaobaiEconomy: compared with s ...

❣💞❣ Database foundation ② 1, 92 syntax join table query 1. Cross connect: corss join -- Cross connect select * from emp cross join dept; 2. natural join Note: if there are multiple fields with the same name, they will be connected equally -- Inner connection select * from emp natural join dept; 3. Using connection: Join using ( ...

Indexes Unique index: a unique index does not allow two rows to have the same index valuePrimary key index: defining a primary key for a table will automatically create a primary key index, which is a special type of unique index. The primary key index requires that each value in the primary key is unique and cannot be emptyClustered index ...