How to choose data types for columns

· Category: SQL & Databases

Short answer

Choose the smallest data type that can represent your domain accurately. Prefer fixed-length types for known sizes, use integers for IDs, and decimals for money.

Steps

  1. Use INT or BIGINT for auto-incrementing IDs based on expected cardinality.
  2. Use VARCHAR for strings with variable length and CHAR for fixed codes.
  3. Use DECIMAL or NUMERIC for monetary values; avoid floating-point types.
  4. Use DATE, TIME, or TIMESTAMP for temporal data.
  5. Use BOOLEAN or TINYINT for flags, depending on database support.

Tips

  • Align data types across related tables to enable efficient joins without implicit conversions.
  • Consider future growth; switching a column from INT to BIGINT later can be expensive.

Common issues

  • Using TEXT or BLOB for short strings wastes memory and disables some indexing features.
  • Storing dates as strings prevents date arithmetic and efficient range queries.r