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SQL Data Modeling Guide (PDF)

SQL Data Modeling Guide — Chapter 9

SQL Syntax

In general, MarkLogic supports the syntax from the SQL92 standard. This chapter describes some of the SQL syntax that are unique to MarkLogic Server.

Supported SQL Statements, Functions and Types

This section describes the SQL statements and functions supported in MarkLogic. The topics are:

Supported Statements

MarkLogic SQL does not support updates, so only the SQL statements in the table below are supported.

SQL Statement Notes
EXPLAIN Produces an execution plan, as described in Execution Plan.
SELECT The following SELECT options are not supported: FULL OUTER JOIN, BLOB types, and correlated subqueries containing a GROUP BY.
CREATE VIEW Creates a view. Views created by this statement only exist for the duration of the SQL connection.
DROP VIEW Drops a view created by CREATE VIEW.

Supported Functions

MarkLogic supports the SQL functions in the SQL92 standard. In addition, MarkLogic supports SQL functions that are not part of the SQL92 standard, as shown in the table below. The SQL functions are listed along with the MarkLogic builtin functions that support them. The syntax for the SQL function is the same as that of the respective builtin function.

You can also call any MarkLogic builtin function in a SQL query, as described in Calling Built-in Functions from SQL.

SQL Function MarkLogic Builtin
acos math:acos
ascii fn:string-to-codepoints
asin math:asin
atan math:atan
atan2 math:atan2
bit-length sql:bit-length
ceiling fn:ceiling
char fn:codepoints-to-string
character-length fn:string-length
char-length fn:string-length
concat fn:concat
cos math:cos
cot math:cot
current-date fn:current-date
current-time fn:current-time
current-timestamp fn:current-dateTime
current-user fn:get-current-user
curdate fn:current-date
curtime fn:current-time
datepart sql:datepart
datediff sql:datediff
dateadd sql:dateadd
day sql:day
dayname sql:dayname
dayofmonth sql:day
dayofweek sql:weekday
dayofyear sql:yearday
degrees math:degrees
exp math:exp
floor fn:floor
hour sql:hours
initcap xdmp:initcap
insert sql:insert
left sql:left
localtime fn:current-time
localtimestamp fn:current-dateTime
locate xdmp:position
log math:log
log10 math:log10
minute sql:minutes
mod math:fmod
month sql:month
monthname sql:monthname
now fn:current-time
octet-length sql:octet-length
pi math:pi
position xdmp:position
power math:pow
quarter sql:quarter
radians math:radians
rand sql:rand
random sql:rand
repeat sql:repeat
right sql:right
sign sql:sign
sin math:sin
second sql:seconds
session-user fn:get-current-user
space sql:space
sqrt math:sqrt
strpos xdmp:position
substring fn:substring
tan math:tan
timestampadd sql:timestampadd
timestampdiff sql:timestampdiff
truncate math:trunc
trunc math:trunc
user xdmp:get-current-user
week sql:week
year sql:year

Supported Types

The table below lists all of the supported SQL types in MarkLogic, along with the mapping from the SQL types to XML Schema (or MarkLogic) types. MarkLogic also supports a number of SQL type that go beyond those supported by the SQL92 standard, as well as some vendor specific types.

Limits on datatypes are not enforced. For example, if you enter DECIMAL(p,s), the precision and scale are ignored.

SQL Type XML Schema Type Range Index (Scalar) Type Notes
CHAR(ACTER) xs:string Fixed length unenforced. CHARACTER SET must be "UTF-8" if specified.
CHAR(ACTER) VARYING / VARCHAR / TEXT xs:string string, anyURI Maximum length unenforced. CHARACTER SET must be "UTF-8" if specified.
NATIONAL CHAR(ACTER) / NCHAR xs:string Fixed length not enforced.
NATIONAL CHAR(ACTER) VARYING / NCHAR VARYING / NVARCHAR xs:string Maximum length not enforced.
NUMERIC / DEC(IMAL) xs:decimal decimal Precision and scale not enforced.
INT(EGER) / MEDIUMINT / INT4 xs:int int
UNSIGNED INT(EGER) / UNSIGNED MEDIUMINT / UNSIGNED INT4 xs:unsignedInt unsignedInt
TINYINT / INT1 xs:byte
UNSIGNED TINYINT / UNSIGNED INT1 xs:unsignedByte
SMALLINT / INT2 xs:short
UNSIGNED SMALLINT / UNSIGNED INT2 xs:unsignedShort
BIGINT / INT8 xs:long long
UNSIGNED BIGINT / UNSIGNED INT8 xs:unsignedLong unsignedLong
FLOAT(X) with X<24 / REAL xs:float float
FLOAT(X) with 24<=X<=52 / DOUBLE (PRECISION) xs:double double
BOOLEAN xs:boolean Not in SQL92
DATE xs:date date DATE does not support a timezone
TIME xs:time time
TIMESTAMP xs:dateTime dateTime, gYearMonth, gYear, gMonth, gDay Oracle converts the g* datatypes to TIMESTAMP WITH TIMEZONE
INTERVAL YEAR / INTERVAL MONTH / INTERVAL YEAR TO MONTH xs:yearMonthDuration yearMonthDuration For INTERVAL types with only year and/or month specified.
INTERVAL DAY / INTERVAL HOUR / INTERVAL DAY TO SECOND etc. xs:dayTimeDuration dayTimeDuration For INTERVAL types with only day / hour / minute / second specified
INTERVAL xs:duration For all other INTERVAL types

System Tables

Data dictionaries consists of a series of tables that are created in the SYS schema. These system tables are listed in the table below.

System Table Description
sys_schemas Lists all of the available schemas.
sys_tables Lists all of the available tables.
sys_columns Lists all of the available columns.
sys_functions Lists all of the available functions.
sys_collations Lists all of the available collations.

To see the full contents of a system table, do a select *. For example:

select * from sys_tables

System Columns __content and __docid

Each view has two system columns:

Column Name Description
__docid Identifies the fragment ID of each document that matches the view(s).
__content Returns the content of document that matches the view(s).

The __docid and __content system columns are preceeded by two underscores.

For example: The following returns the fragment ID for each document that matches the employees view:

select __docid from employees

The following returns the contents of each document that matches the employees view:

select __content from employees

Calling Built-in Functions from SQL

You can call MarkLogic built-in functions from inside a SELECT statement, as long as the parameter types match the column types. You cannot call aggregate functions from SQL.

The following are some examples of the use of MarkLogic functions in SQl statements:

Provide the version of MarkLogic Server and hardware information:

select xdmp_version(), xdmp_platform(), xdmp_architecture()

Trace the performance of a query:

select xdmp_elapsed_time, t1.this, t2.that from t1, t2
    where t1.key=t2.ref group by t1.this

Do some trigonometry:

select math_cos(EmployeeID) from employees

Do some geospatial:

select cts_distance(town.center, building.location) from town, building

Return the first five values of the FirstName column, starting with the third character:

select fn_substring(FirstName,3) from employees limit 5 

MATCH Operator

The MATCH operates differently on range views and template views. You can MATCH column names when using range views, but not template views. You can MATCH on tables created by both range and template views.

When the MATCH operator is used with range views, column names are bound to their corresponding index references and searchable fields are bound to their field names. When the MATCH operator is applied to individual columns, all names are unbound, as it doesn't make sense to constrain searches against one index to the values of another. These queries are executed in unfiltered mode.

The search expression following the MATCH operator must be contained inside single quotes.

Field names, like view and schema names, are treated as case-insensitive for the purposes of duplicate detection and lookup.

Search Grammar

The following table lists the search grammar that can be used by the MATCH operator.

Type Token
Wildcards* ? % *
Boolean Operators AND, OR, NOT, NOT_IN, NEAR/integer
Comparison Operators EQ, NE, LT, LE, GT, GE
Name Binding** <field_name>:<value>, <column_name>:<value>

* To use wildcards in a search expression, you must enable trailing wildcard searches and word lexicons (codepoint collation) on your database.

** Searches are constrained to the named field or column values. The field or column text must have the correct case. For example, 'Position:Manager' is not the same as 'position:Manager'. Because you cannot specify fields in a template view, you cannot MATCH on field names.

Examples

The following queries will work on both range views and template views:

SELECT * FROM employees WHERE employees MATCH 'Manager'

SELECT * FROM employees WHERE employees MATCH 'J*'

SELECT employeeid, firstname, lastname, position FROM employees 
    WHERE employees MATCH 'Steve OR John OR Goodall'

SELECT employeeid, firstname, lastname, position FROM employees 
    WHERE employees MATCH 'Steve AND Manager'

SELECT * from employees WHERE firstname MATCH 'John OR Jane' 
    AND lastname MATCH 'Lead'

The following queries will work on range views only:

SELECT * FROM employees WHERE employees MATCH 'position:Manager'

SELECT firstname, lastname FROM employees WHERE employees 
    MATCH 'employeeid LE 3'

SELECT employeeid, firstname, lastname, position FROM employees 
    WHERE firstname MATCH 'Steve OR John OR Goodall'

SELECT * FROM employees WHERE employees MATCH 'firstname:J*'

SET/SHOW Statements

The MarkLogic ODBC driver supports Postgres SET and SHOW run-time configuration parameters, as well as some parameters that are specific to MarkLogic Server. These parameters only work when accessing MarkLogic through an ODBC driver, as is the case with mlsql. They do not work when accessing MarkLogic through xdmp:sql or the Query Console.

For details on the Postgres parameters, see:

All SET parameters are good for the duration of the SQL session in which they are set. Some parameters are read-only and can only be specified by the SHOW statement. These are described in Read-only SHOW Parameters.

All SET string values must be specified in single quotes (SET parameter 'value').

timezone or time zone

Sets the timezone offset to that for the given timezone name. The standard permitted formats and keywords can be used.

For example, to set the timezone to UTC, enter:

SET timezone 'UTC'

statement_timeout

Sets the timeout for statement execution (milliseconds).

For example:

SET statement_timeout 5000

lc_messages

Sets the locale for error messages.

For example:

SET lc_messages 'en_US'

lc_collate

Sets the default collation in the dynamic environment.

The form we will see from the Postgres client is:

SET lc_collate 'en_US.utf8'

This maps to the collation: http://marklogic.com/collation/en_US

You can also specify a full collation string:

SET lc_collation 'http://marklogic.com/collation/en_US/S1/MO'

lc_numeric

Sets the locale for formatting numeric values.

For example:

set lc_numeric 'de_DE'

lc_time

Sets the locale for formatting date/time values.

For example:

set lc_time 'en_US.UTF-8'

DateType

Sets the output format for dates.

For example:

SET DateType 'ISO'

extra_float_digits

Sets the number of digits displayed for floating point types.

For example:

SET extra_float_digits 2

client_encoding or NAMES

Declares the encoding of data coming from the client.

For example:

SET client_encoding 'UTF8'

SET NAMES is the standard syntax for the same thing.

SET NAMES 'UTF8'

coordinate_system

Set the default coordinate system for geospatial operations.

For example:

SET coordinate_system 'wgs84/double'

For more details, see The Governing Coordinate System and Controlling Coordinate System and Precision in the Search Developer's Guide.

SCHEMA or search_path

Sets the default schema referenced by names in SQL statements.

For example:

SET search_path 'main'

mls_default_xquery

Set the default XQuery version.

For example:

SET mls_default_xquery '1.0-ml'

mls_redundant_check

Enable or disable the redundant check on normal (on full-text) query constraints on rows. Value is 1 (enable) or 0 (disable). The default is 0.

For example:

SET mls_redundant_check 1; 
SELECT title, year FROM songs WHERE year=1991;

Read-only SHOW Parameters

The following parameters can be obtained via the SHOW statement but they are read-only and cannot be set via the SET statement.

Parameter Description
ALL Return values for all the variables with descriptions (columns=name, setting, description).
lc_ctype Return the locale for character classifications. For us this is fixed at zxx.utf8.
max_function_args The limit on the number of function arguments. This will be the value of SQLITE_MAX_FUNCTION_ARG, by default 127.
max_identifier_length The limit on the length of a name. This will be fixed at 64.
max_index_keys The limit on the number of keys in an index. This will be the value of SQLITE_MAX_COLUMN, by default 2000.
integer_datetimes Whether the server supports 64-bit date/time values. Fixed at 1.
server_encoding The encoding the server uses. Fixed at UTF-8.
server_version The version of MarkLogic Server.
server_version_num The version of the server expressed as a single integer.

Best Practices and Performance Considerations

MarkLogic SQL does not have a default/implicit limit for the rows returned. Queries that return large result sets, such as tens of thousands of rows, may perform poorly. Should you experience performance problems it is a best practice to page the results using the LIMIT statement.

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