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1.0 Storage Classes and Datatypes

Each value stored in an SQLite database (or manipulated by the database engine) has one of the following storage classes:

• NULL. The value is a NULL value.

• INTEGER. The value is a signed integer, stored in 1, 2, 3, 4, 6, or 8 bytes depending on the magnitude of the value.

• REAL. The value is a floating point value, stored as an 8-byte IEEE floating point number.

• TEXT. The value is a text string, stored using the database encoding (UTF-8, UTF-16BE or UTF-16LE).

• BLOB. The value is a blob of data, stored exactly as it was input.

Note that a storage class is slightly more general than a datatype. The INTEGER storage class, for example, includes 6 different integer datatypes of different lengths. This makes a difference on disk. But as soon as INTEGER values are read off of disk and into memory for processing, they are converted to the most general datatype (8-byte signed integer). And so for the most part, "storage class" is indistinguishable from "datatype" and the two terms can be used interchangeably.

Any column in an SQLite version 3 database, except an?INTEGER PRIMARY KEY?column, may be used to store a value of any storage class.

All values in SQL statements, whether they are literals embedded in SQL statement text or?parameters?bound toprecompiled SQL statements?have an implicit storage class. Under circumstances described below, the database engine may convert values between numeric storage classes (INTEGER and REAL) and TEXT during query execution.

1.1 Boolean Datatype

SQLite does not have a separate Boolean storage class. Instead, Boolean values are stored as integers 0 (false) and 1 (true).

1.2 Date and Time Datatype

SQLite does not have a storage class set aside for storing dates and/or times. Instead, the built-in?Date And Time Functions?of SQLite are capable of storing dates and times as TEXT, REAL, or INTEGER values:

• TEXT?as ISO8601 strings ("YYYY-MM-DD HH:MM:SS.SSS").
• REAL?as Julian day numbers, the number of days since noon in Greenwich on November 24, 4714 B.C. according to the proleptic Gregorian calendar.
• INTEGER?as Unix Time, the number of seconds since 1970-01-01 00:00:00 UTC.

Applications can chose to store dates and times in any of these formats and freely convert between formats using the built-in date and time functions.

2.0 Type Affinity

In order to maximize compatibility between SQLite and other database engines, SQLite supports the concept of "type affinity" on columns. The type affinity of a column is the recommended type for data stored in that column. The important idea here is that the type is recommended, not required. Any column can still store any type of data. It is just that some columns, given the choice, will prefer to use one storage class over another. The preferred storage class for a column is called its "affinity".

Each column in an SQLite 3 database is assigned one of the following type affinities:

• TEXT
• NUMERIC
• INTEGER
• REAL
• NONE

A column with TEXT affinity stores all data using storage classes NULL, TEXT or BLOB. If numerical data is inserted into a column with TEXT affinity it is converted into text form before being stored.

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A column with NUMERIC affinity may contain values using all five storage classes. When text data is inserted into a NUMERIC column, the storage class of the text is converted to INTEGER or REAL (in order of preference) if such conversion is lossless and reversible. For conversions between TEXT and REAL storage classes, SQLite considers the conversion to be lossless and reversible if the first 15 significant decimal digits of the number are preserved. If the lossless conversion of TEXT to INTEGER or REAL is not possible then the value is stored using the TEXT storage class. No attempt is made to convert NULL or BLOB values.

A string might look like a floating-point literal with a decimal point and/or exponent notation but as long as the value can be expressed as an integer, the NUMERIC affinity will convert it into an integer. Hence, the string '3.0e+5' is stored in a column with NUMERIC affinity as the integer 300000, not as the floating point value 300000.0.

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A column that uses INTEGER affinity behaves the same as a column with NUMERIC affinity. The difference between INTEGER and NUMERIC affinity is only evident in a?CAST expression.

A column with REAL affinity behaves like a column with NUMERIC affinity except that it forces integer values into floating point representation. (As an internal optimization, small floating point values with no fractional component and stored in columns with REAL affinity are written to disk as integers in order to take up less space and are automatically converted back into floating point as the value is read out. This optimization is completely invisible at the SQL level and can only be detected by examining the raw bits of the database file.)

A column with affinity NONE does not prefer one storage class over another and no attempt is made to coerce data from one storage class into another.

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2.1 Determination Of Column Affinity

The affinity of a column is determined by the declared type of the column, according to the following rules in the order shown:

Note that the order of the rules for determining column affinity is important. A column whose declared type is "CHARINT" will match both rules 1 and 2 but the first rule takes precedence and so the column affinity will be INTEGER.

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2.2 Affinity Name Examples

The following table shows how many common datatype names from more traditional SQL implementations are converted into affinities by the five rules of the previous section. This table shows only a small subset of the datatype names that SQLite will accept. Note that numeric arguments in parentheses that following the type name (ex: "VARCHAR(255)") are ignored by SQLite - SQLite does not impose any length restrictions (other than the large global?SQLITE_MAX_LENGTH?limit) on the length of strings, BLOBs or numeric values.

Note that a declared type of "FLOATING POINT" would give INTEGER affinity, not REAL affinity, due to the "INT" at the end of "POINT". And the declared type of "STRING" has an affinity of NUMERIC, not TEXT.

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2.3 Column Affinity Behavior Example

The following SQL demonstrates how SQLite uses column affinity to do type conversions when values are inserted into a table.

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3.0 Comparison Expressions

SQLite version 3 has the usual set of SQL comparison operators including "=", "==", "<", "<=", ">", ">=", "!=", "<>", "IN", "NOT IN", "BETWEEN", "IS", and "IS NOT", .

3.1 Sort Order

The results of a comparison depend on the storage classes of the operands, according to the following rules:

• A value with storage class NULL is considered less than any other value (including another value with storage class NULL).

• An INTEGER or REAL value is less than any TEXT or BLOB value. When an INTEGER or REAL is compared to another INTEGER or REAL, a numerical comparison is performed.

• A TEXT value is less than a BLOB value. When two TEXT values are compared an appropriate collating sequence is used to determine the result.

• When two BLOB values are compared, the result is determined using memcmp().