GUC参数说明
d_format_behavior_compat_options
取值范围：字符串
默认值：''
参数说明：参数值为逗号间隔的字符串，仅允许合法字符串设定，不合法情况下，启动后报error。同样，设置时候，如果新值非法，则报error并且不修改老值。目前可选参数有：
- enable_sbr_identifier：是否允许使用 [] 包裹标识符。开启以后内核原有的数组相关语法会被禁用。
openGauss=# set d_format_behavior_compat_options = 'enable_sbr_identifier';
SET
openGauss=# create table[array](a1 int);
CREATE TABLE
openGauss=# select ARRAY[1,2,3];
ERROR: syntax error at or near "[1,2,3]"
- enable_table_hint_identifier：是否允许table_hint当做标识符，用于列名、变量名等。开启后允许下述hint用作标识符。 涉及的hint有：NOLOCK、READUNCOMMITTED、UPDLOCK、REPEATABLEREAD、SERIALIZABLE、READCOMMITTED、TABLOCK、TABLOCKX、PAGLOCK、ROWLOCK、NOWAIT、READPAST、XLOCK、SNAPSHOT、NOEXPAND。
openGauss=# set d_format_behavior_compat_options = 'enable_table_hint_identifier';
SET
openGauss=# create table testhint(nowait int);
CREATE TABLE
openGauss=# insert into testhint (nowait) values(1);
INSERT 0 1
openGauss=# select max(nowait) from testhint;
max
-----
1
(1 row)
openGauss=# set d_format_behavior_compat_options = '';
SET
openGauss=# create table testhint(nowait int);
ERROR: syntax error at or near "("
LINE 1: create table testhint(nowait int);
^
- enable_abs：是否允许@作为取绝对值操作符使用。opengauss支持在D库下以@object方式声明变量，开启后@为取绝对值操作符。
opengauss=# create table test(@a int, b int);
CREATE TABLE
opengauss=# insert into test values (-1,-2);
INSERT 0 1
opengauss=# select @a from test;
@a
----
-1
(1 row)
opengauss=# set d_format_behavior_compat_options = 'enable_abs';
SET
opengauss=# select @b as abs_b from test;
abs_b
-------
2
(1 row)
ANSI_NULLS
取值范围：on/off
默认值：on
参数说明：用于控制NULL值与非NULL值比较时的表现。如果设置为on，那么NULL值与NULL或者非NULL值做等于或者不等于比较结果都是NULL。如果设置成off，NULL值与NULL值做等于比较结果为true，NULL值与非NULL值做等于比较时结果为false。
openGauss=# set ANSI_NULLS on;
SET
openGauss=# select NULL = NULL;
?column?
----------
(1 row)
openGauss=# select 1 = NULL;
?column?
----------
(1 row)
openGauss=# select NULL <> NULL;
?column?
----------
(1 row)
openGauss=# select 1 <> NULL;
?column?
----------
(1 row)
openGauss=# set ANSI_NULLS off;
SET
openGauss=# select NULL = NULL;
?column?
----------
t
(1 row)
openGauss=# select 1 = NULL;
?column?
----------
f
(1 row)
openGauss=# select NULL <> NULL;
?column?
----------
f
(1 row)
openGauss=# select 1 <> NULL;
?column?
----------
t
(1 row)
IDENTITY_INSERT
取值范围：on/off
默认值：off
参数说明：用于控制在INSERT语句中是否能通过显示指定具有identity属性的列名插入用户提供的值。
openGauss=# show identity_insert;
identity_insert
-----------------
off
(1 row)
openGauss=# create table t_identity_0013(id int identity, name varchar(10));
NOTICE: CREATE TABLE will create implicit sequence "t_identity_0013_id_seq_identity" for serial column "t_identity_0013.id"
CREATE TABLE
openGauss=# insert into t_identity_0013(name) values('zhangsan');
INSERT 0 1
openGauss=# insert into t_identity_0013(id, name) values(100, 'wangwu');
ERROR: Cannot insert identity column "id"
LINE 1: insert into t_identity_0013(id, name) values(100, 'wangwu');
^
openGauss=# set identity_insert=on;
SET
openGauss=# insert into t_identity_0013(id, name) values(100, 'wangwu');
INSERT 0 1
openGauss=# select * from t_identity_0013;
id | name
-----+----------
1 | zhangsan
100 | wangwu
(2 rows)
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