How to Fix ClickHouse Syntax Errors in PostgreSQL

How do I fix a ClickHouse syntax error when running queries in PostgreSQL?

Diagnose and resolve ClickHouse-style syntax errors when running queries in PostgreSQL.

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Description

Why do I get a ClickHouse syntax error in PostgreSQL?

ClickHouse and PostgreSQL have overlapping SQL dialects, but several keywords, functions, and engine clauses exist only in ClickHouse. Running such statements in PostgreSQL triggers a syntax error at or near ... message. Remove or replace ClickHouse-specific syntax before executing the query in Postgres.

Which ClickHouse keywords are invalid in PostgreSQL?

Common offenders include ENGINE, TTL, SAMPLE, FORMAT in INSERT, ARRAY JOIN, and WITH TOTALS.PostgreSQL raises an error because these clauses are undefined in its grammar. Use equivalent PostgreSQL constructs or drop them entirely.

Example

SELECT * FROM Orders SAMPLE 0.1; ⇒ remove SAMPLE or use TABLESAMPLE in Postgres 13+.

How to rewrite ClickHouse CREATE TABLE statements?

ClickHouse adds ENGINE = MergeTree() and ORDER BY outside indexes. PostgreSQL ignores ENGINE and expects ORDER BY only after SELECT.Strip engine clauses and define indexes separately.

-- ClickHouse CREATE TABLE Customers ( id UInt64, name String, email String ) ENGINE = MergeTree() ORDER BY id;. -- PostgreSQL CREATE TABLE customers ( id BIGINT PRIMARY KEY, name TEXT, email TEXT );

How to convert ClickHouse date/time functions?

ClickHouse’s toDateTime() and now64() lack direct PostgreSQL equivalents. Use TO_TIMESTAMP() or NOW(). Cast epochs with TO_TIMESTAMP(epoch).

Can I automate translation?

Use Galaxy’s AI copilot or the open-source clickhouse2postgres formatter to scan queries and suggest compatible syntax.Run unit tests on sample data to confirm behavior.

Best practices for preventing syntax errors

Keep separate SQL files per engine.
Enable strict CI linting with psql -c "EXPLAIN ...".
Add comments noting engine-specific logic.
Use feature flags to switch between dialects.

Why How to Fix ClickHouse Syntax Errors in PostgreSQL is important

How to Fix ClickHouse Syntax Errors in PostgreSQL Example Usage


-- Remove ClickHouse SAMPLE and FORMAT clauses
SELECT c.name,
       SUM(o.total_amount) AS lifetime_value
FROM Customers c
JOIN Orders o ON o.customer_id = c.id
GROUP BY c.name
ORDER BY lifetime_value DESC
LIMIT 10;

How to Fix ClickHouse Syntax Errors in PostgreSQL Syntax


-- SELECT with optional TABLESAMPLE in PostgreSQL
SELECT *
FROM Orders
TABLESAMPLE SYSTEM (10);

-- INSERT without FORMAT clause
INSERT INTO Orders (id, customer_id, order_date, total_amount)
VALUES (1, 101, NOW(), 250.00);

-- Correct date conversion
SELECT TO_TIMESTAMP(order_date) AS order_ts
FROM Orders;

-- Equivalent of ARRAY JOIN using CROSS JOIN LATERAL
SELECT o.id, p.name, oi.quantity
FROM Orders o
JOIN LATERAL (
    SELECT *
    FROM OrderItems oi
    JOIN Products p ON p.id = oi.product_id
    WHERE oi.order_id = o.id
) sub ON TRUE;

Common Mistakes

Leaving ENGINE clauses intact—PostgreSQL does not recognize ENGINE=MergeTree and fails. Remove the clause or translate it into indexes.
Using SAMPLE without TABLESAMPLE—PostgreSQL requires the TABLESAMPLE keyword. Replace SAMPLE 0.1 with TABLESAMPLE SYSTEM (10).