


How Can a PL/pgSQL Function Dynamically Return Results from Various SELECT Queries?
Refactor PL/pgSQL functions to return output of different SELECT queries
Dynamic SQL and return types
Returns records of undefined type
The original function declared a return type of text, but now the goal is to execute the generated SQL statement and return the result as a record. To do this you need to use dynamic SQL and deal with returning records of a type that is not yet defined.
Custom types with numeric and data type mutability
One approach is to create a custom return type with a fixed number of columns but a variable data type. However, this requires defining a list of column definitions for each call, which becomes impractical when the column names and data types are not known in advance.
Use polymorphic types
pg_typeof() Returns the table name as the object identifier type (regtype). When automatically converted to text, identifiers are automatically double-quoted and pattern-qualified, thus preventing SQL injection.
RETURN QUERY EXECUTE
The preferred way to execute dynamic SQL and return rows is RETURN QUERY EXECUTE. It allows you to execute SQL queries and return the results as rowsets with well-defined row types.
Code Example
Suppose you want to return all columns of any table based on the table type parameter:
CREATE OR REPLACE FUNCTION data_of(_tbl_type anyelement, _id int) RETURNS SETOF anyelement LANGUAGE plpgsql AS $func$ BEGIN RETURN QUERY EXECUTE format(' SELECT * FROM %s -- 自动用双引号括起来并进行模式限定 WHERE id = ORDER BY datahora' , pg_typeof(_tbl_type)) USING _id; END $func$;
Usage
Call this function with the table type as the first parameter and the ID as the second parameter. This function will return all columns of the record with the given ID in the specified table.
SELECT * FROM data_of(NULL::pcdmet, 17); -- 将pcdmet替换为任何其他表名。
The above is the detailed content of How Can a PL/pgSQL Function Dynamically Return Results from Various SELECT Queries?. For more information, please follow other related articles on the PHP Chinese website!

MySQL functions can be used for data processing and calculation. 1. Basic usage includes string processing, date calculation and mathematical operations. 2. Advanced usage involves combining multiple functions to implement complex operations. 3. Performance optimization requires avoiding the use of functions in the WHERE clause and using GROUPBY and temporary tables.

Efficient methods for batch inserting data in MySQL include: 1. Using INSERTINTO...VALUES syntax, 2. Using LOADDATAINFILE command, 3. Using transaction processing, 4. Adjust batch size, 5. Disable indexing, 6. Using INSERTIGNORE or INSERT...ONDUPLICATEKEYUPDATE, these methods can significantly improve database operation efficiency.

In MySQL, add fields using ALTERTABLEtable_nameADDCOLUMNnew_columnVARCHAR(255)AFTERexisting_column, delete fields using ALTERTABLEtable_nameDROPCOLUMNcolumn_to_drop. When adding fields, you need to specify a location to optimize query performance and data structure; before deleting fields, you need to confirm that the operation is irreversible; modifying table structure using online DDL, backup data, test environment, and low-load time periods is performance optimization and best practice.

Use the EXPLAIN command to analyze the execution plan of MySQL queries. 1. The EXPLAIN command displays the execution plan of the query to help find performance bottlenecks. 2. The execution plan includes fields such as id, select_type, table, type, possible_keys, key, key_len, ref, rows and Extra. 3. According to the execution plan, you can optimize queries by adding indexes, avoiding full table scans, optimizing JOIN operations, and using overlay indexes.

Subqueries can improve the efficiency of MySQL query. 1) Subquery simplifies complex query logic, such as filtering data and calculating aggregated values. 2) MySQL optimizer may convert subqueries to JOIN operations to improve performance. 3) Using EXISTS instead of IN can avoid multiple rows returning errors. 4) Optimization strategies include avoiding related subqueries, using EXISTS, index optimization, and avoiding subquery nesting.

Methods for configuring character sets and collations in MySQL include: 1. Setting the character sets and collations at the server level: SETNAMES'utf8'; SETCHARACTERSETutf8; SETCOLLATION_CONNECTION='utf8_general_ci'; 2. Create a database that uses specific character sets and collations: CREATEDATABASEexample_dbCHARACTERSETutf8COLLATEutf8_general_ci; 3. Specify character sets and collations when creating a table: CREATETABLEexample_table(idINT

To safely and thoroughly uninstall MySQL and clean all residual files, follow the following steps: 1. Stop MySQL service; 2. Uninstall MySQL packages; 3. Clean configuration files and data directories; 4. Verify that the uninstallation is thorough.

Renaming a database in MySQL requires indirect methods. The steps are as follows: 1. Create a new database; 2. Use mysqldump to export the old database; 3. Import the data into the new database; 4. Delete the old database.


Hot AI Tools

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

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

Undress AI Tool
Undress images for free

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

SublimeText3 Linux new version
SublimeText3 Linux latest version

SecLists
SecLists is the ultimate security tester's companion. It is a collection of various types of lists that are frequently used during security assessments, all in one place. SecLists helps make security testing more efficient and productive by conveniently providing all the lists a security tester might need. List types include usernames, passwords, URLs, fuzzing payloads, sensitive data patterns, web shells, and more. The tester can simply pull this repository onto a new test machine and he will have access to every type of list he needs.

SublimeText3 Chinese version
Chinese version, very easy to use

VSCode Windows 64-bit Download
A free and powerful IDE editor launched by Microsoft

PhpStorm Mac version
The latest (2018.2.1) professional PHP integrated development tool
