Technical Guide to Parsing and Manipulating SQL with JSQLParser

1. Brief description

During the development process, parsing and manipulating SQL is a common requirement, such as dynamically generating SQL, extracting table names, fields in queries, etc. JSQLParser is a powerful open source Java library for parsing SQL and providing syntax tree operation capabilities. It supports most SQL syntax and provides a clear API, simplifying the complexity of SQL operations.

2. Functional characteristics

JSQLParser is a Java-based SQL parsing library that can convert SQL into an actionable syntax tree. It supports the following features:

Analyze SQL: Supports SELECT, INSERT, UPDATE, DELETE and other statements.
Extract information: Get table name, field name, condition, function, etc.
Modify SQL: dynamically add fields, modify conditions, etc.
Supports multiple SQL dialects: compatible with MySQL, PostgreSQL, SQL Server, etc.

Before using JSQLParser, it needs to be added. Here are the Maven dependencies of JSQLParser:

<dependency>
    <groupId></groupId>
    <artifactId>jsqlparser</artifactId>
    <version>4.6</version>
</dependency>

3. Use examples

SQL Monitoring and Audit: Extract sensitive information and perform SQL security checks.
Dynamic SQL construction: Dynamically assemble SQL according to business needs.
Multi-tenant support: Automatically inject tenant fields in SQL.
Complex query optimization: parsing and rewriting SQL queries.

3.1 Analyze and extract SQL information

Extract table names, fields, and WHERE conditions from a SELECT query.

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public class JSQLParserExample {

    public static void main(String[] args) throws JSQLParserException {
        String sql = "SELECT id, name FROM users WHERE age &gt; 18";

        // parse SQL        Select selectStatement = (Select) (sql);
        PlainSelect plainSelect = (PlainSelect) ();

        // Get the table name        String tableName = ().toString();
        ("Table name:" + tableName);

        // Get fields        ().forEach(item -&gt; ("Field:" + item));

        // Get WHERE conditions        ("WHERE Conditions:" + ());
    }
}

3.2 Dynamically modify SQL query conditions

Dynamically add a condition to the WHERE condition of the SQL query.

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public class ModifySQLCondition {

    public static void main(String[] args) throws JSQLParserException {
        String sql = "SELECT * FROM orders WHERE status = 'completed'";

        // parse SQL        Select selectStatement = (Select) (sql);
        PlainSelect plainSelect = (PlainSelect) ();

        // Create new conditions        Expression newCondition = ("amount &gt; 100");

        // Modify WHERE conditions (AND connection)        if (() != null) {
            ((
                () + " AND " + newCondition));
        } else {
            (newCondition);
        }

        // Output modified SQL        ("Modified SQL:" + selectStatement);
    }
}

3.3 Get all table names

Extract all involved table names (including JOIN tables) from complex SQL queries.

import ;
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public class ExtractTableNames {

    public static void main(String[] args) throws JSQLParserException {
        String sql = "SELECT ,  FROM orders a JOIN customers b ON a.customer_id = ";

        // parse SQL        Select selectStatement = (Select) (sql);
        PlainSelect plainSelect = (PlainSelect) ();

        // Main table        ("Main Table:" + ());

        // JOIN table        if (() != null) {
            for (Join join : ()) {
                ("JOIN table:" + ());
            }
        }
    }
}

3.4 Add new fields

Dynamically add a field in the query.

import ;
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public class AddNewField {

    public static void main(String[] args) throws JSQLParserException {
        String sql = "SELECT id, name FROM users";

        // parse SQL        Select selectStatement = (Select) (sql);
        PlainSelect plainSelect = (PlainSelect) ();

        // Add new fields        SelectExpressionItem newField = new SelectExpressionItem();
        (("email"));
        ().add(newField);

        // Output modified SQL        ("Modified SQL:" + selectStatement);
    }
}

3.5 Analyzing complex nested queries

Parses a nested query and extracts all table names and fields.

import ;
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public class ParseNestedSQL {

    public static void main(String[] args) throws JSQLParserException {
        String sql = "SELECT * FROM (SELECT id, name FROM users WHERE age &gt; 18) u WHERE  LIKE 'A%'";

        // parse SQL        Select selectStatement = (Select) (sql);

        // Output SQL structure        ("Resolved SQL:" + selectStatement);
    }
}

4. Summary

JSQLParser is a powerful and flexible SQL parsing tool. Through it, we can easily parse and operate SQL, suitable for dynamic query generation, SQL security audit, multi-tenant injection and other scenarios. In actual development, flexibly using its API according to business needs can significantly improve development efficiency.

Recommended practice:

In a multi-tenant system, use JSQLParser to automatically inject tenant fields.
Combined with JSQLParser to parse SQL logs to achieve accurate SQL performance monitoring.

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