将逗号分割的clob字段转化为varchar，并将字符串拆分为多行

SELECT '远大洪雨' 企业名称,
sgpro.project_name 工程名称,
pur.product_type 产品类别,
pur.product_name 产品名称,
pur.purchase_num 涉及数量,
pur.product_regdate 材料进场时间,
sgpro.build_licence 施工许可证号,
sgpro.contractor_name 总包单位名称
FROM t_purchase_info pur, t_allproject_info sgpro
WHERE pur.project_id = sgpro.id
AND pur.id in (select distinct regexp_substr(ids, '[^,]+', 1, level) project_id
from (select dbms_lob.substr(project_ids) ids
from g_enterprise_score
where class in (3, 4)
and score_type = 5
AND bad_no = 1
AND enterprise_id in
(select distinct id
from bemms.g_enterprise_info
where name like '%远大洪雨%')
and project_ids is not null)
connect by level <=
length(dbms_lob.substr(ids)) -
length(replace(dbms_lob.substr(ids), ',', '')) + 1
)

其中，将clob转化为varchar，利用dbms_lob.substr，例：

select dbms_lob.substr(project_ids)
from g_enterprise_score
where class in (3, 4)
and score_type = 5
AND bad_no = 1
AND enterprise_id in (select distinct id
from bemms.g_enterprise_info
where name like '%远大洪雨%')
and project_ids is not null ;

将一行字符串（逗号分割）转化多行，利用regexp_substr() connect by level，例：

select distinct regexp_substr(ids, '[^,]+', 1, level) project_id
from (select dbms_lob.substr(project_ids) ids
from g_enterprise_score
where class in (3, 4)
and score_type = 5
AND bad_no = 1
AND enterprise_id in (select distinct id
from bemms.g_enterprise_info
where name like '%远大洪雨%')
and project_ids is not null)
connect by level <= length(dbms_lob.substr(ids)) -
length(replace(dbms_lob.substr(ids), ',', '')) + 1

以上SQL执行效率特别低，我们欢欢大神说过： 越是高级的函数越有可能影响效率，还是最基础的函数好，效率杠杠的。

其中尽量少用in，用exists，或者instr，经过优化后的SQL如下：

SELECT '北京XXX股份有限公司' 企业名称,
sgpro.project_name 工程名称,
pur.product_type 产品类别,
pur.product_name 产品名称,
pur.purchase_num 涉及数量,
pur.product_regdate 材料进场时间,
sgpro.build_licence 施工许可证号,
sgpro.contractor_name 总包单位名称
FROM t_purchase_info pur, t_allproject_info sgpro
WHERE pur.project_id = sgpro.id
AND instr((select ',' || wm_concat(dbms_lob.substr(g.project_ids)) || ',' ids
from g_enterprise_score g
where exists (select id
from bemms.g_enterprise_info e
where g.enterprise_id = e.id
and name like '%北京%东方雨虹%')
and (g.class = 3 or g.class = 4)
and g.score_type = 5
AND g.bad_no = 1
and project_ids is not null),
',' || pur.id || ',') > 0