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-<H1 CLASS="western" ALIGN=CENTER>SQLite v3 Value Storage and
-Collation</H1>
-<P>This document is a collection of notes describing the proposed
-SQLite v3 type affinity and collation sequence features.</P>
-<P><FONT color="red">*** Some of the information in this file is obsolete.
-This file is of historical interest only. Do not use this file as a basis
-for new work. ***</FONT></P>
-<H2 CLASS="western">1. Storage Classes</H2>
-<P>Version 2 of SQLite stores all column values as ASCII text.
-Version 3 enhances this by providing the ability to store integer and
-real numbers in a more compact format and the capability to store
-BLOB data.</P>
-<P>Each value stored in an SQLite database (or manipulated by the
-database engine) has one of the following storage classes:</P>
-<UL>
- <LI><P><B>NULL</B>. The value is a NULL value.</P>
- <LI><P><B>INTEGER</B>. The value is a signed integer, stored in 1,
- 2, 4 or 8 bytes depending on the magnitude of the value.</P>
- <LI><P><B>REAL</B>. The value is a floating point value, stored as
- an 8-byte IEEE floating point number.</P>
- <LI><P><B>TEXT</B>. The value is a text string, stored using the
- database encoding (UTF-8, UTF-16BE or UTF-16-LE).</P>
- <LI><P><B>BLOB</B>. The value is a blob of data, stored exactly as
- it was input.</P>
-</UL>
-<P>As in SQLite v2, normally any SQLite v3 column except an INTEGER
-PRIMARY KEY may be used to store any type of value. The exception to
-this rule is described below under 'Strict Affinity Mode'.</P>
-<P>All values supplied to SQLite, whether as literals embedded in SQL
-statements, values bound to pre-compiled SQL statements or data read
-using the COPY command are assigned a storage class before the SQL
-statement is executed. Under circumstances described below, the
-database engine may convert values between numeric storage classes
-(INTEGER and REAL) and TEXT during query execution.
-</P>
-<P>Storage classes are initially assigned as follows:</P>
-<UL>
- <LI><P>Values read using the COPY command are assigned the storage
- class TEXT or NULL.</P>
- <LI><P>Values specified as literals as part of SQL statements are
- assigned storage class TEXT if they are enclosed by single or double
- quotes, INTEGER if the literal is specified as an unquoted number
- with no decimal point or exponent, REAL if the literal is an
- unquoted number with a decimal point or exponent and NULL if the
- value is a NULL.</P>
- <LI><P>Values supplied using the sqlite3_bind_* APIs are assigned
- the storage class that most closely matches the native type bound
- (i.e. sqlite3_bind_blob() binds a value with storage class BLOB).</P>
-</UL>
-<P>The storage class of a value that is the result of an SQL scalar
-operator depends on the outermost operator of the expression.
-User-defined functions may return values with any storage class. It
-is not generally possible to determine the storage class of the
-result of an expression at compile time.</P>
-<H2 CLASS="western">2. Column Affinity</H2>
-<P>Each column in an SQLite 3 database is assigned one of the
-following type affinities:</P>
-<UL>
- <LI><P>TEXT.</P>
- <LI><P>NUMERIC.</P>
- <LI><P>INTEGER.</P>
- <LI><P>NONE.</P>
-</UL>
-<P>The affinity of a column determines the storage class used by
-values inserted into the column.</P>
-<P>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 to text form before being stored.</P>
-<P>A column with NUMERIC affinity may contain values using all five
-storage classes. When text data is inserted into a NUMERIC column, an
-attempt is made to convert it to an integer or real number before it
-is stored. If the conversion is successful, then the value is stored
-using the INTEGER or REAL storage class. If the conversion cannot be
-performed the value is stored using the TEXT storage class. No
-attempt is made to convert NULL or blob values.</P>
-<P>A column that uses INTEGER affinity behaves in the same way as a
-column with NUMERIC affinity, except that if a real value with no
-floating point component (or text value that converts to such) is
-inserted it is converted to an integer and stored using the INTEGER
-storage class.</P>
-<P>A column with affinity NONE makes no attempt to coerce data before
-it is inserted.</P>
-<H3>2.1 Determination Of Column Affinity</H3>
-<P>The type affinity of a column is determined by the declared type
-of the column, according to the following rules:</P>
-<OL>
- <LI><P>If the datatype of the column contains any of the strings
- "CHAR", "CLOB", or "TEXT" then that
- column has TEXT affinity. Notice that the type VARCHAR contains the
- string "CHAR" and is thus assigned TEXT affinity.</P>
- <LI><P>If the datatype contains the string "INT" then it
- is assigned INTEGER affinity.</P>
- <LI><P>If the datatype contains the string "BLOB" is is
- given an affinity of NONE.</P>
- <LI><P>Any column that does not matches the rules above, including
- columns that have no datatype specified, are given NUMERIC affinity.</P>
-</OL>
-<P>If a table is created using a “CREATE TABLE <table> AS
-SELECT...” statement, then all columns have no datatype specified
-and they are given no affinity.</P>
-<H3>2.2 Column Affinity Example</H3>
-<PRE>CREATE TABLE t1(
- t AFFINITY TEXT,
- nu AFFINITY NUMERIC,
- i AFFINITY INTEGER,
- no AFFINITY NONE
-);
-
--- Storage classes for the following row:
--- TEXT, REAL, INTEGER, TEXT
-INSERT INTO t1 VALUES('500.0', '500.0', '500.0', '500.0');
-
--- Storage classes for the following row:
--- TEXT, REAL, INTEGER, REAL
-INSERT INTO t1 VALUES(500.0, 500.0, 500.0, 500.0);</PRE><H2 CLASS="western">
-3. Comparison Expressions</H2>
-<P>Like SQLite v2, v3 features the binary comparison operators '=',
-'<', '<=', '>=' and '!=', an operation to test for set
-membership, 'IN', and the ternary comparison operator 'BETWEEN'.</P>
-<P>The results of a comparison depend on the storage classes of the
-two values being compared, according to the following rules:</P>
-<UL>
- <LI><P>A value with storage class NULL is considered less than any
- other value (including another value with storage class NULL).</P>
- <LI><P>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.</P>
- <LI><P>A TEXT value is less than a BLOB value. When two TEXT values
- are compared, the C library function memcmp() is usually used to
- determine the result. However this can be overriden, as described
- under 'User-defined collation Sequences' below.</P>
- <LI><P>When two BLOB values are compared, the result is always
- determined using memcmp().</P>
-</UL>
-<P>SQLite may attempt to convert values between the numeric storage
-classes (INTEGER and REAL) and TEXT before performing a comparison.
-For binary comparisons, this is done in the cases enumerated below.
-The term “expression” used in the bullet points below means any
-SQL scalar expression or literal other than a column value.</P>
-<UL>
- <LI><P>When a column value is compared to the result of an
- expression, the affinity of the column is applied to the result of
- the expression before the comparison takes place.</P>
- <LI><P>When two column values are compared, if one column has
- INTEGER or NUMERIC affinity and the other does not, the NUMERIC
- affinity is applied to any values with storage class TEXT extracted
- from the non-NUMERIC column.</P>
- <LI><P>When the results of two expressions are compared, the NUMERIC
- affinity is applied to both values before the comparison takes
- place.</P>
-</UL>
-<H3>3.1 Comparison Example</H3>
-<PRE>CREATE TABLE t1(
- a AFFINITY TEXT,
- b AFFINITY NUMERIC,
- c AFFINITY NONE
-);
-
--- Storage classes for the following row:
--- TEXT, REAL, TEXT
-INSERT INTO t1 VALUES('500', '500', '500');
-
--- 60 and 40 are converted to “60” and “40” and values are compared as TEXT.
-SELECT a < 60, a < 40 FROM t1;
-1|0
-
--- Comparisons are numeric. No conversions are required.
-SELECT b < 60, b < 600 FROM t1;
-0|1
-
--- Both 60 and 600 (storage class NUMERIC) are less than '500' (storage class TEXT).
-SELECT c < 60, c < 600 FROM t1;
-0|0</PRE><P>
-In SQLite, the expression “a BETWEEN b AND c” is currently
-equivalent to “a >= b AND a <= c”. SQLite will continue to
-treat the two as exactly equivalent, even if this means that
-different affinities are applied to 'a' in each of the comparisons
-required to evaluate the expression.</P>
-<P>Expressions of the type “a IN (SELECT b ....)” are handled by
-the three rules enumerated above for binary comparisons (e.g. in a
-similar manner to “a = b”). For example if 'b' is a column value
-and 'a' is an expression, then the affinity of 'b' is applied to 'a'
-before any comparisons take place.</P>
-<P>SQLite currently treats the expression “a IN (x, y, z)” as
-equivalent to “a = z OR a = y OR a = z”. SQLite will continue to
-treat the two as exactly equivalent, even if this means that
-different affinities are applied to 'a' in each of the comparisons
-required to evaluate the expression.</P>
-<H2 CLASS="western">4. Operators</H2>
-<P>All mathematical operators (which is to say, all operators other
-than the concatenation operator "||") apply NUMERIC
-affinity to all operands prior to being carried out. If one or both
-operands cannot be converted to NUMERIC then the result of the
-operation is NULL.</P>
-<P>For the concatenation operator, TEXT affinity is applied to both
-operands. If either operand cannot be converted to TEXT (because it
-is NULL or a BLOB) then the result of the concatenation is NULL.</P>
-<H2 CLASS="western">5. Sorting, Grouping and Compound SELECTs</H2>
-<P>When values are sorted by an ORDER by clause, values with storage
-class NULL come first, followed by INTEGER and REAL values
-interspersed in numeric order, followed by TEXT values usually in
-memcmp() order, and finally BLOB values in memcmp() order. No storage
-class conversions occur before the sort.</P>
-<P>When grouping values with the GROUP BY clause values with
-different storage classes are considered distinct, except for INTEGER
-and REAL values which are considered equal if they are numerically
-equal. No affinities are applied to any values as the result of a
-GROUP by clause.</P>
-<P STYLE="font-style: normal">The compound SELECT operators UNION,
-INTERSECT and EXCEPT perform implicit comparisons between values.
-Before these comparisons are performed an affinity may be applied to
-each value. The same affinity, if any, is applied to all values that
-may be returned in a single column of the compound SELECT result set.
-The affinity applied is the affinity of the column returned by the
-left most component SELECTs that has a column value (and not some
-other kind of expression) in that position. If for a given compound
-SELECT column none of the component SELECTs return a column value, no
-affinity is applied to the values from that column before they are
-compared.</P>
-<H2 CLASS="western">6. Other Affinity Modes</H2>
-<P>The above sections describe the operation of the database engine
-in 'normal' affinity mode. SQLite v3 will feature two other affinity
-modes, as follows:</P>
-<UL>
- <LI><P><B>Strict affinity</B> mode. In this mode if a conversion
- between storage classes is ever required, the database engine
- returns an error and the current statement is rolled back.</P>
- <LI><P><B>No affinity</B> mode. In this mode no conversions between
- storage classes are ever performed. Comparisons between values of
- different storage classes (except for INTEGER and REAL) are always
- false.</P>
-</UL>
-<H2 CLASS="western">7. User-defined Collation Sequences</H2>
-<P STYLE="font-style: normal">By default, when SQLite compares two
-text values, the result of the comparison is determined using
-memcmp(), regardless of the encoding of the string. SQLite v3
-provides the ability for users to supply arbitrary comparison
-functions, known as user-defined collation sequences, to be used
-instead of memcmp().</P>
-<P STYLE="font-style: normal"><BR><BR>
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