SQL クエリをフォーマットする方法

问题

SQL クエリが 1 行の長い文字列になっており、レビューとデバッグのために読みやすくする必要があります。

前提条件

• SQL 構文の理解
• クエリ句への習熟

ステップ

1. 1. Parse the SQL query

   The formatter parses the SQL to identify keywords, identifiers, strings, and comments. It recognizes clauses like SELECT, FROM, WHERE, JOIN, GROUP BY, and ORDER BY to determine the structure.

   入力

   SELECT id,name FROM users WHERE age>18 ORDER BY name

   输出

   parsed structure

2. 2. Apply formatting rules

   Place each major clause on a new line. Indent subqueries and join conditions. Align column names in SELECT lists. Use consistent capitalization for keywords (upper or lower based on preference). Add spaces around operators.

   入力

   SELECT id,name FROM users WHERE age>18

   输出

   SELECT id, name\nFROM users\nWHERE age > 18

3. 3. Handle dialect-specific syntax

   Different SQL dialects (PostgreSQL, MySQL, T-SQL) have unique syntax. Choose the correct dialect so the formatter parses functions, types, and keywords correctly. Misidentifying the dialect can cause formatting errors.

   入力

   PostgreSQL query

   输出

   dialect-aware formatting

期待される結果

キーワードの整列、サブクエリのインデント、一貫したスペース配置による読みやすい SQL クエリ。

よくあるエラー

Formatter does not recognize a dialect-specific function

Select the correct SQL dialect. If the formatter still fails, the syntax may be unsupported; use a more capable formatter.

String literals are modified

A good formatter never alters string literal contents. If it does, it has a bug; use a different formatter.

トラブルシューティング指引

• If the formatted query executes differently, compare the original and formatted SQL character by character.
• Comments should be preserved. If they are lost, use a formatter that supports comments.

セキュリティ上の制限

• Formatting SQL does not execute it. However, never format untrusted SQL and then execute it — SQL injection is a separate concern.