描述

CONTEXT用于兼容Oracle数据库连接的上下文操作。在LightDB，CONTEXT为关联的数据库连接定义并记录一个唯一的标签，这样可以通过CONTEXT来管理数据库连接。

命令

参数

例子

以下是使用上下文的一些例子：

sql_context ctx1;
sql_context ctx12;
EXEC SQL CONTEXT ALLOCATE :ctx1;
EXEC SQL CONTEXT USE :ctx1;
EXEC SQL CONNECT TO :usr1;


EXEC SQL CONTEXT ALLOCATE :ctx2;
EXEC SQL CONTEXT USE :ctx2;
EXEC SQL CONNECT TO  :usr2;


EXEC SQL CONTEXT USE :ctx1;
EXEC SQL CONTEXT USE :ctx2;

EXEC SQL CONTEXT USE DEFAULT;

EXEC SQL CONTEXT FREE :ctx1;
EXEC SQL CONTEXT FREE :ctx2;

这里是一个展示使用上下文的例子程序：

int
main(void)
{
	EXEC SQL BEGIN DECLARE SECTION;
	char *dbname     = "testdb";    /* 数据库名 */
	char *user       = "testuser";  /* 连接用户名 */
	char *connection = "tcp:postgresql://localhost:5432/testdb"; /* 连接字符串 */
	char date[64];                  /* 存储日期的缓冲区 */
	EXEC SQL END DECLARE SECTION;
	
	sql_context ctx1;
	sql_context ctx12;
	
	ECPGdebug(1, stderr);
	
	EXEC SQL CONTEXT ALLOCATE :ctx1;
	EXEC SQL CONTEXT USE :ctx1;
	EXEC SQL CONNECT TO :dbname USER :user;
	EXEC SQL ALTER SESSION SET NLS_DATE_FORMAT = 'yyyy::mm::dd';　
	EXEC SQL SELECT sysdate INTO :date;
	printf("sysdate: %s\n", date);
	
	EXEC SQL CONTEXT ALLOCATE :ctx２;
	EXEC SQL CONTEXT USE :ctx2;
	EXEC SQL CONNECT TO :connection USER :user;
	EXEC SQL ALTER SESSION SET NLS_DATE_FORMAT = 'yyyy_mm_dd';　
	EXEC SQL SELECT sysdate INTO :date;
	printf("sysdate: %s\n", date);
	
	EXEC SQL CONTEXT USE :ctx1;
	EXEC SQL SELECT sysdate INTO :date;
	printf("sysdate: %s\n", date);
	
	EXEC SQL CONTEXT USE :ctX2;
	EXEC SQL SELECT sysdate INTO :date;
	printf("sysdate: %s\n", date);
	
	EXEC SQL CONTEXT FREE :ctx1;
	EXEC SQL CONTEXT FREE :ctx2;
	
	return 0;
}

特性说明