Platform and Client Compatibility

Many platforms use the database system. External compatibility of the database system provides a lot of convenience for platforms.

convert_string_to_digit

Parameter description: Specifies the implicit conversion priority, which determines whether to preferentially convert strings into numbers.

This parameter is a USERSET parameter. Set it based on instructions provided in Table 1 GUC parameters.

Value range: Boolean

• on indicates that strings are preferentially converted into numbers.
• off indicates that strings are not preferentially converted into numbers.

Default value: on

NOTICE: Adjusting this parameter will change the internal data type conversion rule and cause unexpected behavior. Exercise caution when performing this operation.

nls_timestamp_format

Parameter description: Specifies the default timestamp format.

This parameter is a USERSET parameter. Set it based on instructions provided in Table 1 GUC parameters.

Value range: a string

Default value: DD-Mon-YYYY HH:MI:SS.FF AM

max_function_args

Parameter description: Specifies the maximum number of parameters allowed for a function.

This parameter is a fixed INTERNAL parameter and cannot be modified.

Value range: an integer.

Default value: 8192

transform_null_equals

Parameter description: Specifies whether expressions of the form expr = NULL (or NULL = expr) are treated as expr IS NULL. They return true if expr evaluates to NULL, and false otherwise.

• The correct SQL-standard-compliant behavior of expr = NULL is to always return null (unknown).
• Filtered forms in Microsoft Access generate queries that appear to use expr = NULL to test for null values. If you enable this parameter, you can use this interface to access the database.

This parameter is a USERSET parameter. Set it based on instructions provided in Table 2 Methods for setting GUC parameters.

Value range: Boolean

• on indicates expressions of the form expr = NULL (or NULL = expr) are treated as expr IS NULL.
• off indicates expr = NULL always returns NULL.

Default value: off

NOTE: New users are always confused about the semantics of expressions involving NULL values. Therefore, off is used as the default value.

support_extended_features

Parameter description: Specifies whether extended database features are supported.

This parameter is a POSTMASTER parameter. Set it based on instructions provided in Table 2 Methods for setting GUC parameters.

Value range: Boolean

• on indicates that extended database features are supported.
• off indicates that extended database features are not supported.

Default value: off

sql_compatibility

Parameter description: Specifies the type of mainstream database with which the SQL syntax and statement behavior of the database is compatible.

This parameter is an INTERNAL parameter. It can be viewed but cannot be modified.

Value range: enumerated values

• A indicates that the database is compatible with the O database.
• B indicates that the database is compatible with the MY database.
• C indicates that the database is compatible with the TD database.
• PG indicates that the database is compatible with the PostgreSQL database.

Default value: A

NOTICE:

• This parameter can be set only by dbcompatibility when you run the CREATE DATABASE command to create a database.
• In the database, this parameter must be set to a specific value. It can be set to A or B and cannot be changed randomly. Otherwise, the setting is not consistent with the database behavior.

enable_set_variables_b_format

Parameter description: Specifies whether the function of customizing user variables is supported in the MY-compatible database.

This parameter is a USERSET parameter. Set it based on instructions provided in Table 1 GUC parameters.

Value range: Boolean

• on indicates that user variables can be customized in the MY-compatible database.
• off indicates that user variables cannot be customized in the MY-compatible database.

behavior_compat_options

Parameter description: Specifies database compatibility behavior. Multiple items are separated by commas (,).

This parameter is a USERSET parameter. Set it based on instructions provided in Table 1 GUC parameters.

Value range: a string

Default value: empty

NOTE:

• Currently, only compatibility configuration items in Table 1 GUC parameters are supported.
• Multiple items are separated by commas (,), for example, set behavior_compat_options='end_month_calculate,display_leading_zero';.

Table 1 Compatibility configuration items

Configuration Item	Behavior
display_leading_zero	Specifies how floating point numbers are displayed. - If this item is not specified, for a decimal number between -1 and 1, the 0 before the decimal point is not displayed. For example, 0.25 is displayed as .25. - If this item is specified, for a decimal number between -1 and 1, the 0 before the decimal point is displayed. For example, 0.25 is displayed as 0.25.
end_month_calculate	Specifies the calculation logic of the add_months function. Assume that the two parameters of the add_months function are param1 and param2, and that the month of param1 and param2 is result. - If this item is not specified, and the Day of param1 indicates the last day of a month shorter than result, the Day in the calculation result will equal that in param1. For example: mogdb=# select add_months('2018-02-28',3) from sys_dummy; add_months ---------------------- 2018-05-28 00:00:00 (1 row) - If this item is specified, and the Day of param1 indicates the last day of a month shorter than result, the Day in the calculation result will equal that in result. For example: mogdb=# select add_months('2018-02-28',3) from sys_dummy; add_months ---------------------- 2018-05-31 00:00:00 (1 row)
compat_analyze_sample	Specifies the sampling behavior of the ANALYZE operation. If this item is specified, the sample collected by the ANALYZE operation will be limited to around 30,000 records, DBnode memory consumption and maintaining the stability of ANALYZE.
bind_schema_tablespace	Binds a schema with the tablespace with the same name. If a tablespace name is the same as sche_name, default_tablespace will also be set to sche_name if search_path is set to sche_name.
bind_procedure_searchpath	Specifies the search path of the database object for which no schema name is specified. If no schema name is specified for a stored procedure, the search is performed in the schema to which the stored procedure belongs. If the stored procedure is not found, the following operations are performed: - If this item is not specified, the system reports an error and exits. - If this item is specified, the search continues based on the settings of search_path. If the issue persists, the system reports an error and exits.
correct_to_number	Controls the compatibility of the to_number() result. If this item is specified, the result of the to_number() function is the same as that of PG11. Otherwise, the result is the same as that of the O database.
unbind_divide_bound	Controls the range check on the result of integer division. If this item is specified, you do not need to check the range of the division result. For example, the result of INT_MIN/(-1) can be INT_MAX+1. If this item is not specified, an out-of-bounds error is reported because the result is greater thanINT_MAX.
return_null_string	Specifies how to display the empty result (empty string ") of the lpad() and rpad() functions. - If this item is not specified, the empty string is displayed as NULL. mogdb=# select length(lpad('123',0,'*')) from sys_dummy; length ---- (1 row) - If this item is specified, the empty string is displayed as single quotation marks ("). mogdb=# select length(lpad('123',0,'*')) from sys_dummy; length ---- 0 (1 row)
compat_concat_variadic	Specifies the compatibility of variadic results of the concat() and concat_ws() functions. If this item is specified and a concat function has a parameter of the variadic type, different result formats in O and Teradata are retained. If this item is not specified and a concat function has a parameter of the variadic type, the result format of O is retained for both O and Teradata. This option has no effect on MY because MY has no variadic type.
merge_update_multi	When MERGE INTO… WHEN MATCHED THEN UPDATE (see MERGE INTO) and INSERT… ON DUPLICATE KEY UPDATE (see INSERT) are used, control the UPDATE behavior if a piece of target data in the target table conflicts with multiple pieces of source data. If this item is specified and the preceding scenario exists, the system performs multiple UPDATE operations on the conflicting row. If this item is not specified and the preceding scenario exists, an error is reported, that is, the MERGE or INSERT operation fails.
hide_tailing_zero	Numeric shows the configuration item. If this parameter is not set, numeric shows the configuration item based on the specified precision. When this parameter is set, hide "0" at the end of the decimal point. set behavior_compat_options='hide_tailing_zero'; select cast(123.123 as numeric(15,10)); numeric ---- 123.123 (1 row)
rownum_type_compat	Specifies the ROWNUM type. The default value is INT8. After this parameter is specified, the value is changed to NUMERIC.
aformat_null_test	Determines the logic for checking whether the row type is not null. When this parameter is set, if a column in a row is not null, true is returned. When this parameter is not set, if all columns in a row are not null, true is returned.
aformat_regexp_match	Determines the matching behavior of regular expression functions. When this parameter is set and sql_compatibility is set to A or B, the options supported by the flags parameter of the regular expression are changed as follows: 1. By default, the character '\n' cannot be matched. 2. When flags contains the n option, the character '\n' can be matched. 3. The regexp_replace(source, pattern replacement) function replaces all matching substrings. 4. regexp_replace(source, pattern, replacement, flags) returns null when the value of flags is “ or null. Otherwise, the meanings of the options supported by the flags parameter of the regular expression are as follows: 1. By default, the character '\n' can be matched. 2. The n option in flags indicates that the multi-line matching mode is used. 3. The regexp_replace(source, pattern replacement) function replaces only the first matched substring. 4. If the value of flags is “ or null, the return value of regexp_replace(source, pattern, replacement, flags) is the character string after replacement.
compat_cursor	Determines the compatibility behavior of implicit cursor states. If this parameter is set and the O compatibility mode is used, the effective scope of implicit cursor states (SQL %FOUND, SQL %NOTFOUND, SQL %ISOPNE and SQL %ROWCOUNT) are extended only the currently executed function to all subfunctions invoked by this function.
proc_outparam_override	Determines the reloading of output parameters of a stored procedure. After this parameter is enabled, the stored procedure can be properly invoked even if only the output parameters of the stored procedure are different.
proc_implicit_for_loop_variable	Determines the behavior of the FOR_LOOP query statement in a stored procedure.When this parameter is set, if rec has been defined in the FOR rec IN query LOOP statement, the defined rec variable is not reused and a new variable is created. Otherwise, the defined rec variable is reused and no new variable is created.
allow_procedure_compile_check	Determines the compilation check of the SELECT and OPEN CURSOR statements in a stored procedure. If this parameter is set, when the SELECT, OPEN CURSOR FOR, CURSOR %rowtype, or for rec in statement is executed in a stored procedure, the stored procedure cannot be created if the queried table does not exist, and the compilation check of the trigger function is not supported. If the queried table exists, the stored procedure is successfully created.
char_coerce_compat	Determines the behavior when char(n) types are converted to other variable-length string types. By default, spaces at the end are omitted when the char(n) type is converted to other variable-length string types. After this parameter is enabled, spaces at the end are not omitted during conversion. In addition, if the length of the char(n) type exceeds the length of other variable-length string types, an error is reported. This parameter is valid only when sql_compatibility is set to A.
pgformat_substr	Controls the performance of substr(str, from, for) in different scenarios. By default, if the value of from is less than 0, substr counts from the end of the string. If the value of for is less than 1, substr returns NULL. After this parameter is enabled, if the value of from is less than 0, substr counts from the first (-from + 1) bit of the character string. If the value of for is less than 0, substr reports an error. This parameter is valid only when sql_compatibility is set to PG.

plpgsql.variable_conflict

Parameter description: Specifies the priority of a stored procedure variable and a table column that have the same name.

This parameter is a USERSET parameter. Set it based on instructions provided in Table 2 Methods for setting GUC parameters.

Value range: String

• error indicates that an error is reported during compilation if the name of a stored procedure variable and that of a table column are the same.
• use_variable indicates that the variable is preferentially used if the name of a stored procedure variable and that of a table column are the same.
• use_column indicates that the column is preferentially used if the name of a stored procedure variable and that of a table column are the same.

Default value: error

td_compatible_truncation

Parameter description: Specifies whether to enable features compatible with a Teradata database. You can set this parameter to on when connecting to a database compatible with the TD database, so that when you perform the INSERT operation, overlong strings are truncated based on the allowed maximum length before being inserted into char- and varchar-type columns in the target table. This ensures all data is inserted into the target table without errors reported.

NOTE: The string truncation function cannot be used if the INSERT statement includes a foreign table. If inserting multi-byte character data (such as Chinese characters) to database with the character set byte encoding (SQL_ASCII, LATIN1), and the character data crosses the truncation position, the string is truncated based on its bytes instead of characters. Unexpected result will occur in tail after the truncation. If you want correct truncation result, you are advised to adopt encoding set such as UTF8, which has no character data crossing the truncation position.

This parameter is a USERSET parameter. Set it based on instructions provided in Table 2 Methods for setting GUC parameters.

Value range: Boolean

• on indicates overlong strings are truncated.
• off indicates overlong strings are not truncated.

Default value: off

uppercase_attribute_name

Parameter description: Specifies whether to return column names in uppercase to the client. This parameter is used only in the ORA-compatible mode and centralized environment.

This parameter is a USERSET parameter. Set it based on instructions provided in Methods for setting GUC parameters.

Value range: Boolean

• on indicates that column names are returned to the client in uppercase.
• off indicates that column names are not returned to the client in uppercase.

Default value: off

lastval_supported

Parameter description: Specifies whether to enable the lastval function.

This parameter is a POSTMASTER parameter. Set it based on instructions provided in Table 1 GUC parameters.

Value range: Boolean

• on indicates that the lastval function is supported. Additionally, the nextval function does not support push-down.
• off indicates that the lastval function is not supported. Additionally, the nextval function supports push-down.

Default value: off