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[英]How to update one column of table with 8 million rows of data in PostgreSQL
[英]How to update a clob column with data over 2 million characters
我正在尝试在 PL/SQL 中更新长度 > 200 万个字符的 clob 值。 我收到错误
字符串字面量太长
有什么办法可以解决这个错误吗?
这是我试图更新 clob 值的 PL/SQL 代码片段:
DECLARE
value clob;
clob_field clob;
fromindex integer;
offset integer;
chunks integer;
eclob clob;
sql_stmt clob;
BEGIN
fromindex := 1;
offset := 2;
clob_field := '<clob_value_with_length_2Million>';
chunks := 1+(dbms_lob.Getlength(clob_field) / 2);
value :='';
FOR chunk IN 1 .. chunks LOOP
IF ( chunk != 1) THEN
value := value || ' || ';
END IF;
value := value || 'to_clob('''||dbms_lob.Substr(clob_field, offset, fromindex)||''')';
fromindex := fromindex + 2;
END LOOP;
dbms_output.put_line(value);
sql_stmt := 'update mytable
set sources = ' || value ||' where scenario_id = 1 and entry_index = 1';
EXECUTE IMMEDIATE sql_stmt;
END;
我在 clob_field 初始化时遇到错误,很明显,因为 PL/SQl 不允许超过 32k 个字符。 所以,我在这里伸出手,看看我是否可以解决我的问题。
如果您使用绑定变量,则可以减少所需的代码量并提高代码的性能。 如果您每次都尝试构建不同的更新语句,那么数据库将需要为每个不同的查询提供一个执行计划。 使用绑定变量还无需执行任何 SQL 清理以防止 SQL 注入。
SQL> CREATE TABLE mytable
2 AS
3 SELECT 1 AS scenario_id, 1 AS entry_index, EMPTY_CLOB () || 'clob1' AS sources FROM DUAL
4 UNION ALL
5 SELECT 2 AS scenario_id, 2 AS entry_index, EMPTY_CLOB () || 'clob2' AS sources FROM DUAL;
Table created.
SQL> SELECT * FROM mytable;
SCENARIO_ID ENTRY_INDEX SOURCES
----------- ----------- --------------------------------------------------------------------------------
1 1 clob1
2 2 clob2
SQL> DECLARE
2 clob_field CLOB;
3 l_scenario_id NUMBER;
4 l_entry_index NUMBER;
5 sql_stmt CLOB;
6 BEGIN
7 clob_field := '<clob_value_with_length_2Million>';
8 l_scenario_id := 1;
9 l_entry_index := 1;
10
11 sql_stmt :=
12 'update mytable set sources = :bind_clob where scenario_id = :scenario and entry_index = :entry';
13
14 EXECUTE IMMEDIATE sql_stmt
15 USING clob_field, l_scenario_id, l_entry_index;
16 END;
17 /
PL/SQL procedure successfully completed.
SQL> SELECT * FROM mytable;
SCENARIO_ID ENTRY_INDEX SOURCES
----------- ----------- --------------------------------------------------------------------------------
1 1 <clob_value_with_length_2Million>
2 2 clob2
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