How to Convert String to Date in Redshift

Galaxy Glossary

How do I convert a string to a DATE in Amazon Redshift?

Transforms VARCHAR date strings into DATE values using TO_DATE, CAST, or CONVERT.

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Description

Why convert a string to DATE in Redshift?

Storing dates as DATE lets Redshift run date math, use partitions, and speed filters. VARCHAR dates block these optimizations.

What functions convert a string to DATE?

Use TO_DATE(text, format) for flexible parsing, or CAST(string AS DATE)/CONVERT(DATE, string) when the text is already in ISO-8601 (YYYY-MM-DD).

How does TO_DATE work?

TO_DATE matches each format specifier (YYYY, MM, DD, HH24) to the input.Mismatches return NULL, so verify patterns.

Example: parse US style date

SELECT TO_DATE('04/15/2024','MM/DD/YYYY'); -- 2024-04-15

How to cast ISO strings directly?

If the string is '2024-04-15', simply SELECT '2024-04-15'::DATE; or CAST('2024-04-15' AS DATE);

Can I convert while loading?

Apply TO_DATE in a COPY command’s timeformat or inside a SELECT ...INSERT staging query to avoid post-load fixes.

How to update an existing VARCHAR column?

1) Add a new DATE column.
2) UPDATE the new column with TO_DATE.
3) Drop the old column, or swap names.

Best practices for string-to-date conversion

• Store dates in ISO-8601 to permit plain casts.
• Validate with REGEXP_LIKE before casting to cut NULLs.
• Document the expected format in ETL code.

What if parsing fails?

TO_DATE returns NULL, so add a WHERE filter or COALESCE to flag bad rows: WHERE TO_DATE(raw_date,'DD-Mon-YYYY') IS NULL.

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Why How to Convert String to Date in Redshift is important

How to Convert String to Date in Redshift Example Usage


-- Convert order_date stored as text to DATE and calculate monthly revenue
SELECT DATE_TRUNC('month', TO_DATE(order_date_txt,'YYYY-MM-DD'))   AS month,
       SUM(total_amount)                                           AS monthly_sales
FROM   Orders
GROUP  BY 1
ORDER  BY 1;

How to Convert String to Date in Redshift Syntax


TO_DATE(string, format) → DATE
    • string: VARCHAR holding the date.
    • format: format mask using Redshift date patterns.

CAST(string AS DATE) or string::DATE → DATE
    • Works when string is in 'YYYY-MM-DD' only.

CONVERT(DATE, string) → DATE
    • Synonym for CAST.

Example masks:
    'MM/DD/YYYY'   -- 04/15/2024
    'DD-Mon-YYYY'  -- 15-Apr-2024
    'YYYYMMDD'     -- 20240415

Common Mistakes

Relying on CAST for non-ISO strings. CAST only works with 'YYYY-MM-DD'. Use TO_DATE with a matching format for other patterns.
Ignoring bad rows. TO_DATE returns NULL on mismatch; SUM or COUNT then drop those rows silently. Add validation or COALESCE to detect issues.

Frequently Asked Questions (FAQs)

Does TO_DATE support time zones?

No. TO_DATE returns a DATE without time zone. Use TO_TIMESTAMP for date-time values.

Can I store dates as INTEGER (YYYYMMDD)?

You can, but querying is slower and code becomes harder. Native DATE types enable date functions and compression.

Is there a performance cost to TO_DATE in queries?

Yes, minor CPU overhead. Prefer pre-casting during ETL so production queries scan DATE columns directly.

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