pgsql是 PostgreSQL 数据库的简称,而is null是 SQL 语言中的一个条件判断,用于检查某个字段的值是否为 NULL(空值)。下面我将详细解释这个概念及其相关内容。 基础概念 NULL 值:在数据库中,NULL 表示缺失或未知的数据。它不同于空字符串或零,因为它表示的是“无”或“未知”的状态。
if (!$result) { echo "query did not execute"; } if ($line = pg_fetch_assoc($result)) { if ($line['rows'] == 0) { echo "0 records"} } else { while ($row = pg_fetch_array($result)) {//do stuff with $row} }?> This solution doesn't raise the load of the system wi...
static int PQsendQueryInternal(PGconn *conn, const char *query, bool newQuery) { PGcmdQueueEntry *entry = NULL; if (!PQsendQueryStart(conn, newQuery)) return 0; if (!query) { /* check the argument */ appendPQExpBufferStr(&conn->errorMessage, libpq_gettext("command string is a nu...
socketFactory String null Specify a socket factory for socket creation socketFactoryArg (deprecated) String null Argument forwarded to constructor of SocketFactory class. autosave String never Specifies what the driver should do if a query fails, possible values: always, never, conservative cleanupSavep...
A list of actual argument value expressions must appear if and only if the cursor was declared to take arguments. These values will be substituted in the query. The query plan for a bound cursor is always considered cacheable; there is no equivalent of EXECUTE in this case. Notice that ...
鉴于以上规则,在PL/pgSQL里直接出现的SQL命令必须在每次执行时均引用相同的表和字段,换句话说,不能将函数的参数用作SQL命令的表名或字段名。如果想绕开该限制,可以考虑使用PL/pgSQL中的EXECUTE语句动态地构造命令,由此换来的代价是每次执行时都要构造一个新的命令计划。
variable_name [CONSTANT] variable_type [NOT NULL] [ {DEFAULT|:=} expression ]; 1). SQL中的数据类型均可作为PL/pgSQL变量的数据类型,如integer、varchar和char等。 2). 如果给出了DEFAULT子句,该变量在进入BEGIN块时将被初始化为该缺省值,否则被初始化为SQL空值。缺省值是在每次进入该块时进行计算的。
{ // 先暂停任务 再删除 SysScheduleTrigger scheduleTrigger = sysScheduleTriggerMapper.selectById(id); if (Objects.isNull(scheduleTrigger)) { // 该任务不存在 throw new MyException(500, "该任务不存在", ""); } int result = sysScheduleTriggerMapper.deleteById(id); // 删除任务 schedulerDelete(...
NULL; Dynamic SQL To generate dynamic commands that can involve different tables or different data types each time they are run from a PL/pgSQL stored procedure, use theEXECUTEstatement. EXECUTEcommand-string[ INTO target ]; In the preceding,command-stringis an expression yielding a string (of...
socketFactory String null Specify a socket factory for socket creation socketFactoryArg (deprecated) String null Argument forwarded to constructor of SocketFactory class. autosave String never Specifies what the driver should do if a query fails, possible values: always, never, conservative cleanupSavep...