Data Types

MemSQL supports the following data types. The sizes given are for in-memory rowstore tables. Columnstore (on-disk) tables are stored differently, and often compressed.

Integer Numbers

Data Type Size Size (Not Null) Synonyms Min Value Max Value
BOOL* (see note below) 2 bytes 1 byte BOOLEAN -128 127
BIT 9 bytes 8 bytes
TINYINT 2 bytes 1 byte -128 127
SMALLINT 4 bytes 2 bytes -32768 32767
MEDIUMINT 4 bytes 3 bytes -8388608 8388607
INT 8 bytes 4 bytes INTEGER -2147483648 2147483647
BIGINT 12 bytes 8 bytes -2 ** 63 (2 ** 63) - 1


  • BOOL and BOOLEAN are synonymous with TINYINT. A value of 0 is considered FALSE, non-zero values are considered TRUE.

Each integer type can be “unsigned”, doubling the positive range of values and disallowing values under 0.

Real Numbers

Data Type Size Size (Not Null) Synonyms Precision
DOUBLE 8 bytes 8 bytes REAL 24 to 53 bits
FLOAT 4 bytes 4 bytes 23 bits
DECIMAL see note see note DEC, FIXED, NUMERIC 65 digits

The space consumed by the DECIMAL datatype varies with the precision and scale arguments. The syntax for defining a DECIMAL (or its synonyms DEC, FIXED, and NUMERIC) is in the form DECIMAL(P, S) where P is the total number of digits (precision) and S (scale) is how many of those digits appear after the decimal point. For example, DECIMAL(10,5) will store numbers with 5 digits before the decimal and 5 after.

The formula is ceil(P / 9) * 4. In our example, it would be ceil(10 / 9) * 4, or 8 bytes.

Time and Date

Data Type Size Size (Not Null) Resolution Min Value Max Value
DATE 8 bytes 4 bytes day 1000-01-01 9999-12-31
TIME 8 bytes 4 bytes second -838:59:59 838:59:59
DATETIME 12 bytes 8 bytes second 1000-01-01 00:00:00 9999-12-31 23:59:59
DATETIME(6) 12 bytes 8 bytes microsecond 1000-01-01 00:00:00.000000 9999-12-31 23:59:59.999999
YEAR 2 bytes 1 byte year 1901 2155

Timestamp Behavior

The TIMESTAMP and TIMESTAMP(6) types support automatic initialization and update of timestamp values. If you don’t need automatic initialization or update support, it is recommended that you use the DATETIME or DATETIME(6) types instead. The size and resolution of TIMESTAMP and TIMESTAMP(6) are the same as DATETIME and DATETIME(6), respectively.

By default, the first field in a table declared as TIMESTAMP behaves the same as one defined with DEFAULT CURRENT_TIMESTAMP and ON UPDATE CURRENT_TIMESTAMP. Or, alternatively, if the first TIMESTAMP type field is declared as a TIMESTAMP(6), then it behaves as if it was defined with both DEFAULT CURRENT_TIMESTAMP(6) and UPDATE CURRENT_TIMESTAMP(6).

If any column other than the first TIMESTAMP column is updated, then the TIMESTAMP column is also updated to the value of CURRENT_TIMESTAMP. If a row is inserted in the table and no value is provided for the first TIMESTAMP field, that field defaults to the CURRENT_TIMESTAMP value. If the first timestamp-type column is a TIMESTAMP(6), the behavior is similar except that the higher-resolution timestamp CURRENT_TIMESTAMP(6) is used.

For example, see below how the value of the ts column is chosen after insert and update operations:

memsql> CREATE TABLE r(d DATETIME(6), ts TIMESTAMP(6), id INT);

memsql> INSERT r(d, id) VALUES("2017-07-01", 1);

memsql> SELECT * FROM r;
| d                          | ts                         | id   |
| 2017-07-01 00:00:00.000000 | 2017-05-09 23:32:38.815242 |    1 |

memsql> UPDATE r SET id = 2 WHERE id = 1;

memsql> SELECT * FROM r;
| d                          | ts                         | id   |
| 2017-07-01 00:00:00.000000 | 2017-05-09 23:33:53.549569 |    2 |

The behavior where the first TIMESTAMP or TIMESTAMP(6) column has the current time value inserted or updated automatically is deprecated in the MemSQL 6 release and will be removed in a future release. For new application development, explicitly use DEFAULT CURRENT_TIMESTAMP and ON UPDATE CURRENT_TIMESTAMP in column definitions for timestamp if you want this behavior. For example:

  id INT);

String Types

Fixed-Length String

There are three fixed-size string types in MemSQL. The space consumed is directly proportional to their length definitions. Values of type CHAR require 3 x LENGTH bytes of memory, as MemSQL supports only the UTF8 character set. Values of type BINARY require LENGTH bytes of memory.

Data Type Size Size (Not Null)
CHAR(LENGTH) 3*LENGTH + 4 bytes 3*LENGTH bytes

Variable-Length Strings

There are several variable-length string types. The data for these variable types are stored in a memory allocation designed for them, and pointers to their locations in memory are stored in the main table structure. This means that the space consumed by a particular value is the byte length of the string, plus an 8-byte overhead for the pointer, and a 4-byte overhead for storing the length. (There is an additional 4-byte overhead if the field is nullable.) One exception is values less than 7 bytes long. Those small values are stored directly in the pointer area.

The three main types are VARCHAR, VARBINARY, and LONGTEXT. While they all operate similarly for most English-language alphanumeric strings, there are several important differences in their behavior. The length limit of the VARCHAR is measured in Unicode characters, not in bytes. VARBINARY fields store data verbatim, regardless of whether they are valid Unicode strings. Sorting and comparing a VARBINARY uses the exact binary representation.

Data Type Max Length
VARCHAR 21,845 characters

There are several variants of the BLOB and TEXT types, listed below. Aside from their maximum lengths, there is no practical difference between these types in MemSQL, including performance or memory efficiency. They are implemented solely for backwards compatibility with MySQL syntax.

Name Max Length Description
BLOB 65,535 bytes VARBINARY
TEXT 65,535 bytes LONGTEXT


The JSON type can contain any valid Javascript Object Notation data, including maps, arrays, and nested types. For more information see the JSON Guide .

Data Type Size Size (Not Null)
JSON 20 bytes + data size 16 bytes + data size

Geospatial Types

Geospatial types contain information about points, paths, and polygons on the surface of the Earth. For more information, see the Geospatial Guide.

Data Type Size Size (Not Null)
GEOGRAPHYPOINT 8 bytes 8 bytes

The space consumed by the path and polygon data in Geography columns is dependent on the complexity of the objects. Very roughly, a Geography value consumes 24 bytes per vertex, plus a 64 byte overhead, plus some minor overhead for each “ring” in a multipolygon.

Indexing a Geography object may also consume more space than indexes over other datatypes. The rule of thumb is 40 bytes * the value of the RESOLUTION parameter of the index, per row.

MemSQL Procedural SQL (MPSQL) Types

Two data types are only supported in MemSQL Procedural SQL (MPSQL) scalar-valued functions and stored procedures: ARRAY and RECORD. The QUERY data type is only supported in stored procedures. For more information about these types, see the ARRAY, RECORD, and QUERY topics.

Other Types

Data Type Size Size (Not Null) Max cardinality Max values per row
ENUM 4 bytes 2 bytes 65,535 unique values 1
SET 12 bytes 8 bytes 64 unique values 64

Comparing mismatched datatypes

Using comparisons between mismatched datatypes may degrade query performance and may use unsafe type conversions which can yield undesirable query results. MemSQL will display a warning for queries with potentially problematic comparisons between mismatched datatypes in the EXPLAIN and information_schema records for the query.

These warnings do not necessarily indicate a problem, and you may have valid reasons for comparing different datatypes. But these type mismatches are flagged to help you identify potential problems that you may not be aware of.

When you see these warnings, you should check whether the datatypes are expected to be different. You may wish to consider changing the datatypes of the fields or values involved. You may also wish to consider adding explicit type conversion operations, such as the cast operators or functions like STR_TO_DATE which convert between different types.

These warnings can be seen in EXPLAIN <query>, information_schema.plancache.plan_warnings, information_schema.mv_queries.plan_warnings, and the PlanWarnings column of show plancache in textual form, as well as in EXPLAIN JSON <query>, information_schema.plancache.plan_info, and information_schema.mv_queries.plan_info in JSON form.


An example of these warnings is the following:


| EXPLAIN                                                                                                                                                                                                                                                                |
| WARNING: Comparisons between mismatched datatypes which may involve unsafe datatype conversions and/or degrade performance. Consider changing the datatypes, or adding explicit typecasts. See for more information. |
|                                                                                                                                                                                                                                                                        |
| WARNING: Comparison between mismatched datatypes: (`t`.`id` = 123). Types 'varchar(50) CHARACTER SET utf8 COLLATE utf8_general_ci NOT NULL' vs 'bigint(20) NOT NULL'.                                                                                                  |
|                                                                                                                                                                                                                                                                        |
| Gather partitions:all alias:remote_0                                                                                                                                                                                                                                   |
| Project []                                                                                                                                                                                                                                                         |
| Filter [ = 123]                                                                                                                                                                                                                                                    |
| TableScan db.t, PRIMARY KEY (id)                                                                                                                                                                                                                                       |

In this example, the query involves the expression t.i = 123, where t.i is a string field. When a numeric value is compared to a string, the string is converted to a numeric value, e.g. the string '123' is converted to the number 123.

This comparison may be problematic for multiple reasons:

  • The mismatched datatypes may indicate a mistake in how the query is written or how the table is defined. The query may behave differently than intended and yield undesired results. For example, all of the strings '123', '123.0', '0123', and '123abc' compare equal to the integer 123, so while the query may be intended to retrieve a single row with the specified id, this equality comparison may actually yield multiple rows whose id values all compare equal to 123.

  • The mismatched datatypes negatively impact performance of the query. If the field and constant were either both strings or both integers, the query plan would be able to use the index to efficiently seek to lookup the matching id. But because there are actually many possible string ids that match the number 123, which do not come in any particular order in terms of string lexicographic order, the query cannot seek into the index and instead must scan all the rows of the table.

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