What's the best data type for each column in your database?

1 Numeric data types

Numeric data types are used to store numbers, such as integers, decimals, or fractions. They can be further classified into exact and approximate numeric types, depending on how precisely they represent the values. Exact numeric types, such as INTEGER, SMALLINT, or DECIMAL, store the exact value of the number, without any rounding or truncation. Approximate numeric types, such as FLOAT, REAL, or DOUBLE PRECISION, store an approximation of the number, with some possible loss of precision. You should use exact numeric types when you need to store exact values, such as IDs, counts, or prices. You should use approximate numeric types when you need to store large or very small numbers, such as scientific measurements, or when you don't need exact precision, such as averages or ratios.

2 Character data types

Character data types are used to store text, such as names, addresses, or descriptions. They can be further classified into fixed-length and variable-length character types, depending on how much space they allocate for the values. Fixed-length character types, such as CHAR or NCHAR, allocate a fixed amount of space for each value, regardless of its actual length. Variable-length character types, such as VARCHAR or NVARCHAR, allocate only the space needed for each value, plus some overhead. You should use fixed-length character types when you know the exact length of the values, such as codes, abbreviations, or flags. You should use variable-length character types when you don't know the exact length of the values, or when they vary significantly, such as names, emails, or comments.

3 Date and time data types

Date and time data types are used to store dates, times, or both. They can be further classified into absolute and relative date and time types, depending on how they represent the values. Absolute date and time types, such as DATE, TIME, or TIMESTAMP, store a specific point in time, such as a birthday, an appointment, or a transaction. Relative date and time types, such as INTERVAL or DURATION, store a period of time, such as a duration, a difference, or a recurrence. You should use absolute date and time types when you need to store events, schedules, or histories. You should use relative date and time types when you need to store durations, intervals, or frequencies.

4 Boolean data types

Boolean data types are used to store logical values, such as true or false. They can be further classified into simple and complex boolean types, depending on how they represent the values. Simple boolean types, such as BOOLEAN or BIT, store a single bit of information, either 0 or 1, true or false. Complex boolean types, such as ENUM or SET, store a combination of multiple bits of information, representing a set of possible values, such as yes or no, on or off, or red, green, or blue. You should use simple boolean types when you need to store binary choices, such as flags, indicators, or switches. You should use complex boolean types when you need to store multiple choices, such as options, preferences, or categories.

5 Binary data types

Binary data types are used to store raw data, such as images, files, or encrypted data. They can be further classified into fixed-length and variable-length binary types, depending on how much space they allocate for the values. Fixed-length binary types, such as BINARY or RAW, allocate a fixed amount of space for each value, regardless of its actual length. Variable-length binary types, such as VARBINARY or BLOB, allocate only the space needed for each value, plus some overhead. You should use fixed-length binary types when you know the exact length of the values, such as hashes, keys, or signatures. You should use variable-length binary types when you don't know the exact length of the values, or when they vary significantly, such as images, videos, or documents.

6 Other data types

Besides the above-mentioned data types, there are some other data types that are specific to certain database systems, such as JSON, XML, or GEOGRAPHY. These data types are used to store complex or structured data, such as objects, documents, or locations. They can offer some advantages, such as native support, validation, or indexing, but they can also have some drawbacks, such as compatibility, portability, or performance issues. You should use these data types when you need to store data that is not easily represented by the standard data types, or when you need to leverage the features of the database system. However, you should also be aware of the potential limitations and challenges of using these data types.

7 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?