decode function

Single-line functions-character Functions Although each database supports SQL statements, each database also has operation functions supported by each database. These are single-row functions. If you want to develop a database, in addition to SQL,

1. Select the most efficient table name order (valid only in the Rule-based optimizer) The SQL Server parser processes the table names in the FROM clause in Right-to-left order, therefore, the last table in the FROM clause (driving table) is

The first step is to establish an appropriate index. SQL does not add a function in the index field to ensure that the cable is effective. If the composite index is noted in the Order of SQL. If an index is already present, it is recommended that

Sometimes when we show the data in the table, we need to display the rows into columns, as in the following form:The original table structure is shown below:---------------------------Product Name Sales Quarter---------------------------Cheese 50

1. Select the most efficient table name order (valid only in the rule-based optimizer ) The parser for SQL Server processes the table names in the FROM clause in a right-to-left order, so the table that is written in the FROM clause (the underlying

The DECODE function is Oracle PL/SQL is one of the most powerful functions, and only Oracle SQL provides this function, and the SQL implementations of other database vendors do not yet have this function. What is the use of decode? Let's first

SQL Optimization Tips (1):Connection order in the WHERE clause: Oracle parses the WHERE clause in a bottom-up order, and according to this principle, the connections between tables must be written before other where conditions, those that can filter

Struggled for several nights debugging procedures, wrote several blog, and finally set up a mybatis configuration extension mechanism. While it is important to extend the mechanism, it is at least less inspiring if there are no truly useful

1. Understand the Implementation plan1-1. What is the execution planWhen an Oracle database executes an SQL statement, the Oracle optimizer determines the execution path of the SQL statement according to certain rules. To ensure that SQL statements

Select the most efficient table name orderThe Oracle parser processes the table names in the FROM clause in a right-to-left order, and the FROM clause is written in the final table (the underlying table, driving tables) will be processed first, and

In most cases, Oracle uses index t to traverse tables more quickly, and the optimizer improves performance primarily based on defined indexes.However, if the SQL code written in the WHERE clause of the SQL statement is not reasonable, it will cause

Oracle Common Functions--trunc,to_date,to_char,to_number, SUBSTR,REPLACE,NVL, Trim,wm_concat,upper, Lower,length,add_months ( sysdate,1)View Oracle Version: SELECT * from V$version First, trunc function1, TRUNC (for dates) The date value that the

  Where can I start learning about Oracle? Here, I will take you to the door of Oracle. One chapter a day, seven days of entry is not a dream. 1. SQL language Overview 1.1 SQL language classification Data Definition Language (DDL) Used to CREATE,

In Oracle, you can use the decode function to convert rows to columns. For example, if you have A student table named A: IDNAMESUBJECTSCORE1 Zhang San Language 902 Zhang San mathematics 803 Li Si. In Oracle, you can use the decode function to

Document directory Nvl Decode Function Decode is an exclusive function provided by Oracle. It is a powerful function. Although it is not an SQLStandard, but very useful for performance. Up to now, other database vendors have not yet provided

7.Reduce the number of database accesses When each SQL statement is executed, ORACLE performs a lot of internal work: parsing SQL statements, estimating index utilization, binding variables, and reading data blocks. it can be seen that reducing the

  Oracle provides a number of logical judgment functions that can be used in queries.     1, testing for null values-NVL function     function prototype: NVL (testvalue,substitutevalue)     common usage is   Select max (score) from SC Where name= '

The Oracle decode function, regardless of whether the result of the query satisfies ' PRIMARY ', is executed by the SELECT statement in the parameter, and you know by looking at the execution planSet Autotrace traceonlyselect decode(database_role

in Oracle, case and then and decode usage one. Case... then syntax: – Writing one: CaseWhen value 1 then return value 1 when value 2 then return value 2ElseDefault Value – two: CaseWhen condition 1 then return value 1 when condition 2 then return

1.oracle OptimizerThe goal of optimization is divided into 4 categories:Choose (optional)Rule (rules-based)First rows (line one)All rows (all rows)Description: Describe the execution plan for SQLObject owner: Objects SchemaObject Name: Objects