How to Migrate from ClickHouse to SQL Server

How do I migrate data from ClickHouse to SQL Server?

Export data from ClickHouse and import it into SQL Server while preserving schema, data types, and indexes.

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Description

What is the fastest way to move data from ClickHouse to SQL Server?

Dump ClickHouse tables to CSV or Parquet with clickhouse-client, copy files to the SQL Server host, then run BULK INSERT or an SSIS package to load them. This minimizes network overhead and lets you parallel-load large tables.

Which migration steps should I follow?

1) Export schema
2) Map data types
3) Export data
4) Create target tables
5) Bulk load data
6) Recreate indexes & constraints
7) Validate counts & checksums

How do I export ClickHouse tables?

Use clickhouse-client --query="SELECT * FROM Orders FORMAT CSV" > orders.csv. Repeat for each table or script multiple queries in parallel for speed.

How do I create matching tables in SQL Server?

Translate ClickHouse types: UInt32 → INT, DateTime64 → DATETIME2, Decimal(18,2) → DECIMAL(18,2). Always set NOT NULL where ClickHouse columns lacked nullability.

What is the recommended bulk-load command?

BULK INSERT Orders FROM 'C:\data\orders.csv' WITH (FORMAT='CSV', FIRSTROW=2, FIELDTERMINATOR=',', ROWTERMINATOR='\n', TABLOCK). Use CHECK_CONSTRAINTS and ERRORFILE for safer loads.

How do I test the migration?

After loading, run row counts: SELECT COUNT(*) FROM Orders in both systems. For deeper checks, compare MD5 of sorted primary-key & critical numeric columns.

When should I migrate indexes & FKs?

Add them only after data loads finish; doing so earlier slows BULK INSERT drastically.

Can I automate the process?

Yes. Wrap each step in PowerShell or Python, use sqlcmd for DDL, and parallelize exports with GNU parallel to hit near-wire speed.

Best practices for zero-downtime cutover?

Replicate last-minute changes with incremental exports (WHERE updated_at >= :last_sync), schedule a short freeze, replay deltas, swap application connection strings, and monitor error rates.

Why How to Migrate from ClickHouse to SQL Server is important

How to Migrate from ClickHouse to SQL Server Example Usage


-- Migrate Products table
clickhouse-client --query="SELECT id, name, price, stock FROM Products FORMAT CSV" > products.csv

CREATE TABLE Products (
  id    INT            PRIMARY KEY,
  name  NVARCHAR(255)  NOT NULL,
  price DECIMAL(10,2)  NOT NULL,
  stock INT            NOT NULL
);

BULK INSERT Products
FROM 'C:\data\products.csv'
WITH (FORMAT='CSV', FIRSTROW=2, FIELDTERMINATOR=',', ROWTERMINATOR='\n');

How to Migrate from ClickHouse to SQL Server Syntax


-- 1. Export from ClickHouse
clickhouse-client \
  --query="SELECT id, customer_id, order_date, total_amount FROM Orders FORMAT CSV" \
  > orders.csv

-- 2. Create table in SQL Server
CREATE TABLE Orders (
  id           INT            PRIMARY KEY,
  customer_id  INT            NOT NULL,
  order_date   DATETIME2      NOT NULL,
  total_amount DECIMAL(18,2)  NOT NULL
);

-- 3. Bulk load into SQL Server
BULK INSERT Orders
FROM 'C:\data\orders.csv'
WITH (
  FORMAT            = 'CSV',
  FIRSTROW          = 2,
  FIELDTERMINATOR   = ',',
  ROWTERMINATOR     = '\n',
  TABLOCK
);

Common Mistakes

Ignoring data-type mismatches: Loading a ClickHouse <code>UInt64</code> into SQL Server <code>INT</code> overflows silently. Always map to <code>BIGINT</code> or <code>DECIMAL</code>.
Keeping indexes enabled during <code>BULK INSERT</code>: This makes large loads 10× slower. Drop or disable indexes, load data, then rebuild.