Database Schema Diff
Compare two database schemas (DDL dumps) and generate a structural diff plus a dependency-ordered ALTER TABLE migration script. Detects added/dropped/changed tables, columns, types, constraints, and indexes; flags data-loss operations. Multi-dialect (ANSI/MySQL/PostgreSQL/SQLite/T-SQL). 100% client-side.
About Database Schema Diff
Compare two database schemas (DDL dumps) and generate a structural diff plus a dependency-ordered ALTER TABLE migration script. Detects added/dropped/changed tables, columns, types, constraints, and indexes; flags data-loss operations. Multi-dialect (ANSI/MySQL/PostgreSQL/SQLite/T-SQL). 100% client-side. Everything runs locally in your browser — your data never leaves your device.
How to use
- Enter your input in the tool above.
- Adjust any options to your preference.
- Use the Copy or Download buttons to save the result.
- Everything happens locally — your data never leaves your browser.
FAQ
How does the schema diff tool work?
Paste two DDL scripts (source and target). The tool parses every CREATE TABLE and CREATE INDEX statement into a normalized schema model — tables, columns (type, nullability, default), primary/foreign/unique/check constraints, and indexes. It then diffs the two models and emits an ALTER TABLE migration script that brings source in line with target, in correct dependency order.
What kinds of changes are detected?
Added/removed tables, added/removed columns, column type changes, nullability changes, default-value changes, added/removed primary/foreign/unique/check constraints, and added/removed indexes. Each change is color-coded (green for added, red for removed, amber for modified) and destructive operations get a data-loss warning badge.
How are foreign-key dependencies ordered in the migration?
We topologically sort tables by their foreign-key references. Tables are created in dependency order (referenced tables first) and dropped in reverse order. Foreign-key constraints are added after both endpoints exist, and indexes are created last — so the generated script runs cleanly without 'table does not exist' errors.
Does it flag data-loss operations?
Yes. Dropping a table, dropping a column, narrowing a type (e.g. VARCHAR(255) → VARCHAR(50), INT → SMALLINT), making a NOT-NULL column without a default, and dropping a default all produce a warning badge in the diff view and a `-- ⚠ DATA LOSS` comment in the generated migration script.
What extra features does this tool have compared to others?
(1) Multi-dialect DDL parsing (ANSI/MySQL/PostgreSQL/SQLite/T-SQL). (2) Bidirectional migration (source→target and target→source). (3) Topological FK dependency ordering. (4) Data-loss warnings on destructive ops. (5) Type-widening vs narrowing detection. (6) Ignore options (case, column order, whitespace). (7) Diff summary stats (added/removed/changed counts). (8) Filter by object type (table/column/constraint/index). (9) Copy / download .sql migration. (10) localStorage history (max 20). (11) Shareable URL. (12) Side-by-side change tree with color coding. No DB connection required.
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