PostgreSQL 自定義函數處理特殊需求

工作中，在某些特殊需求下，基本的SQL語句已經不能滿足業務需求，需要使用函數來處理。

1. 需要新建sequence。由於部分表已經有數據，這時，新建的sequence的起始位置不能從1開始。

CREATE OR REPLACE FUNCTION create_sequence(sequence_name character varying, table_name character varying, column_name character varying)
  --sequence_name 是需要新建的sequence名稱
  --table_name 是sequence作用的表
  --column_name 是統計當前表的數據量的列值
  RETURNS bigint AS
$BODY$
    DECLARE 
    startNum int8;
    createsequence "varchar" := '';
    selectsequence "varchar" := '';

    BEGIN
	    --先獲取當面表中已經保存了多少數據
        selectsequence := 'select COALESCE(max('||column_name||'), 0) + 1 FROM '|| table_name ||'';
		--將查詢出來的結果放入startNum中
	execute selectsequence into startNum;
        --聲明 創建 sequence的語句。
        createsequence := 'CREATE SEQUENCE '||sequence_name||'
	 INCREMENT 1
	 MINVALUE 1
	 MAXVALUE 9223372036854775807
	 START '|| startNum ||' 
	 CACHE 1';
	--執行創建sequence的SQL語句
	execute createsequence;
	 
        RETURN startNum;
    END;
$BODY$
  LANGUAGE plpgsql VOLATILE
  COST 100;
ALTER FUNCTION create_sequence(character varying, character varying, character varying) OWNER TO postgres;

2. 需求，需要將這兩行數據 每列相加。

初始數據：

結果爲

2.1 先將將string轉換爲數組。如1,2,3,4,5轉換爲 [1,2,3,4,5]

CREATE OR REPLACE FUNCTION tools_str2array(_originstr text)
  RETURNS integer[] AS
$BODY$
declare _cindex INTEGER;
declare _arrIndex INTEGER;
DECLARE _arr_str int4[];
DECLARE _tmp_str VARCHAR(10);
DECLARE _delimeter VARCHAR(1);
BEGIN
_arrIndex:=1;
_cindex:=1;
_delimeter:=',';

--_strres:=_strres||'原始字符串是：'||_originStr;

while _cindex<"length"(_originStr) loop
--_strres :=_strres||'【這個是什麼？】'||split_part(_originStr, _delimeter, _arrIndex);
_tmp_str:=split_part(_originStr, _delimeter, _arrIndex);
if "character_length"(_tmp_str)<1 then
exit;
end if;
_arr_str:=_arr_str|| CAST(_tmp_str as int4);
_arrIndex:=_arrIndex+1;
END loop;
return _arr_str;
end;
$BODY$
  LANGUAGE plpgsql VOLATILE
  COST 100;
ALTER FUNCTION tools_str2array(text) OWNER TO postgres;

2.2. 新增聚集函數。

CREATE AGGREGATE hot_map_test(
BASETYPE = TEXT,--輸入值
SFUNC = csk_test_start,--最初執行的函數
STYPE = TEXT[],--輸出類型
FINALFUNC = count_hot_map--最後執行的函數
);

2.3 新建計算函數 計算結果

CREATE AGGREGATE count_test(
BASETYPE = TEXT,
SFUNC = csk_test_start,
STYPE = TEXT[],
FINALFUNC = count_hot_map
);

CREATE OR REPLACE FUNCTION csk_test_start(a text[], s text)
  RETURNS text[] AS
$BODY$
BEGIN
RETURN a || s;
END;
$BODY$
  LANGUAGE plpgsql VOLATILE
  COST 100;
ALTER FUNCTION csk_test_start(text[], text) OWNER TO postgres;

CREATE OR REPLACE FUNCTION count_hot_map(text[])
  RETURNS integer[] AS
$BODY$
    DECLARE 
    startNum int8;
    spilt_sql "varchar" := '';
    selectsequence "varchar" := '';
	temp_array int4[];
	result_array int4[];

    BEGIN
        for index in 1..array_length($1 , 1) loop
			spilt_sql = 'select tools_str2Array('''||$1[index]||''')';
			execute spilt_sql into temp_array;
			
			for array_items_index in 1..array_length(temp_array, 1) loop
				if result_array[array_items_index] is null then
				   result_array[array_items_index] = 0;
				end if;  
   
				result_array[array_items_index] = result_array[array_items_index] + temp_array[array_items_index];
			end loop;
		end loop;
    RETURN result_array;
    END;
$BODY$
  LANGUAGE plpgsql VOLATILE
  COST 100;
ALTER FUNCTION count_hot_map(text[]) OWNER TO postgres;