{"id":2700,"date":"2025-03-12T23:58:23","date_gmt":"2025-03-12T15:58:23","guid":{"rendered":"https:\/\/www.laixuexila.com\/?p=2700"},"modified":"2025-03-12T23:58:23","modified_gmt":"2025-03-12T15:58:23","slug":"postgresql-%e5%b8%b8%e7%94%a8%e5%87%bd%e6%95%b0","status":"publish","type":"post","link":"https:\/\/www.laixuexila.com\/index.php\/2025\/03\/12\/postgresql-%e5%b8%b8%e7%94%a8%e5%87%bd%e6%95%b0\/","title":{"rendered":"PostgreSQL \u5e38\u7528\u51fd\u6570"},"content":{"rendered":"\n<p>PostgreSQL \u63d0\u4f9b\u4e86\u5927\u91cf\u7684\u5185\u5efa\u51fd\u6570\uff0c\u8fd9\u4e9b\u51fd\u6570\u652f\u6301\u5404\u79cd\u5e38\u89c1\u7684\u6570\u636e\u5904\u7406\u4efb\u52a1\uff0c\u5e2e\u52a9\u5f00\u53d1\u8005\u5b8c\u6210\u4ece\u5b57\u7b26\u4e32\u64cd\u4f5c\u5230\u6570\u636e\u7c7b\u578b\u8f6c\u6362\u7b49\u5404\u79cd\u64cd\u4f5c\u3002\u4ee5\u4e0b\u662f PostgreSQL \u5e38\u7528\u51fd\u6570\u7684\u8be6\u7ec6\u5206\u7c7b\u548c\u4f7f\u7528\u4ecb\u7ecd\uff1a<\/p>\n\n\n\n<h2 class=\"wp-block-heading\"><strong>1. \u6570\u5b66\u51fd\u6570<\/strong><\/h2>\n\n\n\n<h3 class=\"wp-block-heading\"><strong>1.1 <code>ABS(x)<\/code><\/strong><\/h3>\n\n\n\n<p>\u8fd4\u56de\u6570\u503c <code>x<\/code> \u7684\u7edd\u5bf9\u503c\u3002<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>SELECT ABS(-10);  -- \u8fd4\u56de 10<\/code><\/pre>\n\n\n\n<h3 class=\"wp-block-heading\"><strong>1.2 <code>CEIL(x)<\/code> \u6216 <code>CEILING(x)<\/code><\/strong><\/h3>\n\n\n\n<p>\u8fd4\u56de\u5927\u4e8e\u6216\u7b49\u4e8e <code>x<\/code> \u7684\u6700\u5c0f\u6574\u6570\u3002<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>SELECT CEIL(4.3);  -- \u8fd4\u56de 5<\/code><\/pre>\n\n\n\n<h3 class=\"wp-block-heading\"><strong>1.3 <code>FLOOR(x)<\/code><\/strong><\/h3>\n\n\n\n<p>\u8fd4\u56de\u5c0f\u4e8e\u6216\u7b49\u4e8e <code>x<\/code> \u7684\u6700\u5927\u6574\u6570\u3002<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>SELECT FLOOR(4.7);  -- \u8fd4\u56de 4<\/code><\/pre>\n\n\n\n<h3 class=\"wp-block-heading\"><strong>1.4 <code>ROUND(x, n)<\/code><\/strong><\/h3>\n\n\n\n<p>\u5c06\u6570\u5b57 <code>x<\/code> \u56db\u820d\u4e94\u5165\u5230\u5c0f\u6570\u70b9\u540e <code>n<\/code> \u4f4d\u3002<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>SELECT ROUND(4.5678, 2);  -- \u8fd4\u56de 4.57<\/code><\/pre>\n\n\n\n<h3 class=\"wp-block-heading\"><strong>1.5 <code>POWER(x, y)<\/code><\/strong><\/h3>\n\n\n\n<p>\u8fd4\u56de <code>x<\/code> \u7684 <code>y<\/code> \u6b21\u5e42\u3002<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>SELECT POWER(2, 3);  -- \u8fd4\u56de 8<\/code><\/pre>\n\n\n\n<h3 class=\"wp-block-heading\"><strong>1.6 <code>SQRT(x)<\/code><\/strong><\/h3>\n\n\n\n<p>\u8fd4\u56de\u6570\u5b57 <code>x<\/code> \u7684\u5e73\u65b9\u6839\u3002<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>SELECT SQRT(16);  -- \u8fd4\u56de 4<\/code><\/pre>\n\n\n\n<h3 class=\"wp-block-heading\"><strong>1.7 <code>RANDOM()<\/code><\/strong><\/h3>\n\n\n\n<p>\u8fd4\u56de\u4e00\u4e2a\u4ecb\u4e8e 0 \u548c 1 \u4e4b\u95f4\u7684\u968f\u673a\u6d6e\u52a8\u6570\u503c\u3002<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>SELECT RANDOM();  -- \u8fd4\u56de\u4e00\u4e2a\u968f\u673a\u503c\uff0c\u5982 0.456789<\/code><\/pre>\n\n\n\n<h3 class=\"wp-block-heading\"><strong>1.8 <code>PI()<\/code><\/strong><\/h3>\n\n\n\n<p>\u8fd4\u56de\u5e38\u6570 <code>\u03c0<\/code> \u7684\u503c\u3002<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>SELECT PI();  -- \u8fd4\u56de 3.14159265358979<\/code><\/pre>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h2 class=\"wp-block-heading\"><strong>2. \u5b57\u7b26\u4e32\u51fd\u6570<\/strong><\/h2>\n\n\n\n<h3 class=\"wp-block-heading\"><strong>2.1 <code>CONCAT(str1, str2, ...)<\/code><\/strong><\/h3>\n\n\n\n<p>\u8fde\u63a5\u591a\u4e2a\u5b57\u7b26\u4e32\u3002<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>SELECT CONCAT('Hello', ' ', 'World');  -- \u8fd4\u56de 'Hello World'<\/code><\/pre>\n\n\n\n<h3 class=\"wp-block-heading\"><strong>2.2 <code>LENGTH(str)<\/code><\/strong><\/h3>\n\n\n\n<p>\u8fd4\u56de\u5b57\u7b26\u4e32 <code>str<\/code> \u7684\u957f\u5ea6\u3002<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>SELECT LENGTH('Hello');  -- \u8fd4\u56de 5<\/code><\/pre>\n\n\n\n<h3 class=\"wp-block-heading\"><strong>2.3 <code>LOWER(str)<\/code><\/strong><\/h3>\n\n\n\n<p>\u5c06\u5b57\u7b26\u4e32 <code>str<\/code> \u8f6c\u4e3a\u5c0f\u5199\u3002<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>SELECT LOWER('Hello');  -- \u8fd4\u56de 'hello'<\/code><\/pre>\n\n\n\n<h3 class=\"wp-block-heading\"><strong>2.4 <code>UPPER(str)<\/code><\/strong><\/h3>\n\n\n\n<p>\u5c06\u5b57\u7b26\u4e32 <code>str<\/code> \u8f6c\u4e3a\u5927\u5199\u3002<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>SELECT UPPER('Hello');  -- \u8fd4\u56de 'HELLO'<\/code><\/pre>\n\n\n\n<h3 class=\"wp-block-heading\"><strong>2.5 <code>TRIM([LEADING | TRAILING | BOTH] trim_character FROM str)<\/code><\/strong><\/h3>\n\n\n\n<p>\u79fb\u9664\u5b57\u7b26\u4e32\u4e24\u7aef\u7684\u7a7a\u683c\u6216\u6307\u5b9a\u5b57\u7b26\u3002<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>SELECT TRIM(' ' FROM '  Hello  ');  -- \u8fd4\u56de 'Hello'<\/code><\/pre>\n\n\n\n<h3 class=\"wp-block-heading\"><strong>2.6 <code>REPLACE(str, old_substring, new_substring)<\/code><\/strong><\/h3>\n\n\n\n<p>\u5728\u5b57\u7b26\u4e32 <code>str<\/code> \u4e2d\u66ff\u6362 <code>old_substring<\/code> \u4e3a <code>new_substring<\/code>\u3002<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>SELECT REPLACE('Hello World', 'World', 'PostgreSQL');  -- \u8fd4\u56de 'Hello PostgreSQL'<\/code><\/pre>\n\n\n\n<h3 class=\"wp-block-heading\"><strong>2.7 <code>POSITION(substring IN str)<\/code><\/strong><\/h3>\n\n\n\n<p>\u8fd4\u56de\u5b50\u5b57\u7b26\u4e32 <code>substring<\/code> \u5728\u5b57\u7b26\u4e32 <code>str<\/code> \u4e2d\u7684\u4f4d\u7f6e\u3002<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>SELECT POSITION('l' IN 'Hello');  -- \u8fd4\u56de 3<\/code><\/pre>\n\n\n\n<h3 class=\"wp-block-heading\"><strong>2.8 <code>SUBSTRING(str FROM start FOR length)<\/code><\/strong><\/h3>\n\n\n\n<p>\u8fd4\u56de\u4ece <code>str<\/code> \u5f00\u59cb\u7684\u6307\u5b9a\u957f\u5ea6\u7684\u5b50\u5b57\u7b26\u4e32\u3002<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>SELECT SUBSTRING('Hello' FROM 2 FOR 3);  -- \u8fd4\u56de 'ell'<\/code><\/pre>\n\n\n\n<h3 class=\"wp-block-heading\"><strong>2.9 <code>REVERSE(str)<\/code><\/strong><\/h3>\n\n\n\n<p>\u8fd4\u56de\u5b57\u7b26\u4e32\u7684\u53cd\u8f6c\u3002<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>SELECT REVERSE('Hello');  -- \u8fd4\u56de 'olleH'<\/code><\/pre>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h2 class=\"wp-block-heading\"><strong>3. \u65e5\u671f\u548c\u65f6\u95f4\u51fd\u6570<\/strong><\/h2>\n\n\n\n<h3 class=\"wp-block-heading\"><strong>3.1 <code>CURRENT_DATE<\/code><\/strong><\/h3>\n\n\n\n<p>\u8fd4\u56de\u5f53\u524d\u65e5\u671f\u3002<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>SELECT CURRENT_DATE;  -- \u8fd4\u56de '2025-03-12'<\/code><\/pre>\n\n\n\n<h3 class=\"wp-block-heading\"><strong>3.2 <code>CURRENT_TIME<\/code><\/strong><\/h3>\n\n\n\n<p>\u8fd4\u56de\u5f53\u524d\u65f6\u95f4\u3002<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>SELECT CURRENT_TIME;  -- \u8fd4\u56de '14:30:45'<\/code><\/pre>\n\n\n\n<h3 class=\"wp-block-heading\"><strong>3.3 <code>CURRENT_TIMESTAMP<\/code><\/strong><\/h3>\n\n\n\n<p>\u8fd4\u56de\u5f53\u524d\u65f6\u95f4\u6233\uff08\u5305\u62ec\u65e5\u671f\u548c\u65f6\u95f4\uff09\u3002<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>SELECT CURRENT_TIMESTAMP;  -- \u8fd4\u56de '2025-03-12 14:30:45'<\/code><\/pre>\n\n\n\n<h3 class=\"wp-block-heading\"><strong>3.4 <code>NOW()<\/code><\/strong><\/h3>\n\n\n\n<p>\u8fd4\u56de\u5f53\u524d\u65f6\u95f4\u6233\uff08\u4e0e <code>CURRENT_TIMESTAMP<\/code> \u76f8\u540c\uff09\u3002<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>SELECT NOW();  -- \u8fd4\u56de '2025-03-12 14:30:45'<\/code><\/pre>\n\n\n\n<h3 class=\"wp-block-heading\"><strong>3.5 <code>AGE(timestamp, timestamp)<\/code><\/strong><\/h3>\n\n\n\n<p>\u8fd4\u56de\u4e24\u4e2a\u65f6\u95f4\u6233\u4e4b\u95f4\u7684\u95f4\u9694\u3002<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>SELECT AGE('2025-03-12', '1990-01-01');  -- \u8fd4\u56de '35 years 2 mons 11 days'<\/code><\/pre>\n\n\n\n<h3 class=\"wp-block-heading\"><strong>3.6 <code>EXTRACT(field FROM source)<\/code><\/strong><\/h3>\n\n\n\n<p>\u4ece\u65e5\u671f\u6216\u65f6\u95f4\u4e2d\u63d0\u53d6\u6307\u5b9a\u90e8\u5206\uff08\u5982\u5e74\u3001\u6708\u3001\u65e5\u3001\u5c0f\u65f6\u7b49\uff09\u3002<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>SELECT EXTRACT(YEAR FROM CURRENT_DATE);  -- \u8fd4\u56de\u5f53\u524d\u5e74\u4efd<\/code><\/pre>\n\n\n\n<h3 class=\"wp-block-heading\"><strong>3.7 <code>TO_DATE(string, format)<\/code><\/strong><\/h3>\n\n\n\n<p>\u5c06\u5b57\u7b26\u4e32\u8f6c\u6362\u4e3a\u65e5\u671f\u3002<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>SELECT TO_DATE('2025-03-12', 'YYYY-MM-DD');  -- \u8fd4\u56de '2025-03-12'<\/code><\/pre>\n\n\n\n<h3 class=\"wp-block-heading\"><strong>3.8 <code>TO_TIMESTAMP(string, format)<\/code><\/strong><\/h3>\n\n\n\n<p>\u5c06\u5b57\u7b26\u4e32\u8f6c\u6362\u4e3a\u65f6\u95f4\u6233\u3002<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>SELECT TO_TIMESTAMP('2025-03-12 14:30:45', 'YYYY-MM-DD HH24:MI:SS');  -- \u8fd4\u56de '2025-03-12 14:30:45'<\/code><\/pre>\n\n\n\n<h3 class=\"wp-block-heading\"><strong>3.9 <code>DATE_TRUNC(field, source)<\/code><\/strong><\/h3>\n\n\n\n<p>\u5c06\u65e5\u671f\u6216\u65f6\u95f4\u6233\u622a\u65ad\u5230\u6307\u5b9a\u7684\u7c92\u5ea6\u3002<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>SELECT DATE_TRUNC('year', CURRENT_DATE);  -- \u8fd4\u56de '2025-01-01 00:00:00'<\/code><\/pre>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h2 class=\"wp-block-heading\"><strong>4. JSON \u548c JSONB \u51fd\u6570<\/strong><\/h2>\n\n\n\n<h3 class=\"wp-block-heading\"><strong>4.1 <code>JSONB_BUILD_OBJECT(key, value, ...)<\/code><\/strong><\/h3>\n\n\n\n<p>\u521b\u5efa\u4e00\u4e2a <code>JSONB<\/code> \u5bf9\u8c61\u3002<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>SELECT JSONB_BUILD_OBJECT('name', 'John', 'age', 30);  -- \u8fd4\u56de '{\"name\": \"John\", \"age\": 30}'<\/code><\/pre>\n\n\n\n<h3 class=\"wp-block-heading\"><strong>4.2 <code>JSONB_ARRAY_LENGTH(jsonb)<\/code><\/strong><\/h3>\n\n\n\n<p>\u8fd4\u56de <code>JSONB<\/code> \u6570\u7ec4\u7684\u957f\u5ea6\u3002<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>SELECT JSONB_ARRAY_LENGTH('&#91;1, 2, 3]'::jsonb);  -- \u8fd4\u56de 3<\/code><\/pre>\n\n\n\n<h3 class=\"wp-block-heading\"><strong>4.3 <code>JSONB_SET(jsonb, path, new_value)<\/code><\/strong><\/h3>\n\n\n\n<p>\u4fee\u6539 <code>JSONB<\/code> \u5bf9\u8c61\u4e2d\u7684\u67d0\u4e2a\u503c\u3002<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>SELECT JSONB_SET('{\"name\": \"John\", \"age\": 30}'::jsonb, '{age}', '35');  -- \u8fd4\u56de '{\"name\": \"John\", \"age\": 35}'<\/code><\/pre>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h2 class=\"wp-block-heading\"><strong>5. \u805a\u5408\u51fd\u6570<\/strong><\/h2>\n\n\n\n<h3 class=\"wp-block-heading\"><strong>5.1 <code>COUNT(*)<\/code><\/strong><\/h3>\n\n\n\n<p>\u8fd4\u56de\u7b26\u5408\u6761\u4ef6\u7684\u884c\u6570\u3002<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>SELECT COUNT(*) FROM employees;  -- \u8fd4\u56de\u5458\u5de5\u603b\u6570<\/code><\/pre>\n\n\n\n<h3 class=\"wp-block-heading\"><strong>5.2 <code>SUM(column)<\/code><\/strong><\/h3>\n\n\n\n<p>\u8fd4\u56de\u67d0\u5217\u7684\u603b\u548c\u3002<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>SELECT SUM(salary) FROM employees;  -- \u8fd4\u56de\u6240\u6709\u5458\u5de5\u7684\u5de5\u8d44\u603b\u548c<\/code><\/pre>\n\n\n\n<h3 class=\"wp-block-heading\"><strong>5.3 <code>AVG(column)<\/code><\/strong><\/h3>\n\n\n\n<p>\u8fd4\u56de\u67d0\u5217\u7684\u5e73\u5747\u503c\u3002<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>SELECT AVG(salary) FROM employees;  -- \u8fd4\u56de\u5458\u5de5\u7684\u5e73\u5747\u5de5\u8d44<\/code><\/pre>\n\n\n\n<h3 class=\"wp-block-heading\"><strong>5.4 <code>MIN(column)<\/code><\/strong><\/h3>\n\n\n\n<p>\u8fd4\u56de\u67d0\u5217\u7684\u6700\u5c0f\u503c\u3002<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>SELECT MIN(salary) FROM employees;  -- \u8fd4\u56de\u6700\u4f4e\u5de5\u8d44<\/code><\/pre>\n\n\n\n<h3 class=\"wp-block-heading\"><strong>5.5 <code>MAX(column)<\/code><\/strong><\/h3>\n\n\n\n<p>\u8fd4\u56de\u67d0\u5217\u7684\u6700\u5927\u503c\u3002<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>SELECT MAX(salary) FROM employees;  -- \u8fd4\u56de\u6700\u9ad8\u5de5\u8d44<\/code><\/pre>\n\n\n\n<h3 class=\"wp-block-heading\"><strong>5.6 <code>GROUP_CONCAT()<\/code><\/strong><\/h3>\n\n\n\n<p>\u8fd4\u56de\u4e00\u4e2a\u5b57\u7b26\u4e32\uff0c\u5b83\u7531\u7ec4\u5185\u6bcf\u4e00\u884c\u7684\u503c\u8fde\u63a5\u800c\u6210\u3002<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>SELECT STRING_AGG(name, ', ') FROM employees;  -- \u8fd4\u56de\u6240\u6709\u5458\u5de5\u59d3\u540d\u7684\u9017\u53f7\u5206\u9694\u5217\u8868<\/code><\/pre>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h2 class=\"wp-block-heading\"><strong>6. \u6761\u4ef6\u51fd\u6570<\/strong><\/h2>\n\n\n\n<h3 class=\"wp-block-heading\"><strong>6.1 <code>COALESCE(value, ...)<\/code><\/strong><\/h3>\n\n\n\n<p>\u8fd4\u56de\u5217\u8868\u4e2d\u7684\u7b2c\u4e00\u4e2a\u975e <code>NULL<\/code> \u503c\u3002<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>SELECT COALESCE(NULL, NULL, 'First', 'Second');  -- \u8fd4\u56de 'First'<\/code><\/pre>\n\n\n\n<h3 class=\"wp-block-heading\"><strong>6.2 <code>NULLIF(value1, value2)<\/code><\/strong><\/h3>\n\n\n\n<p>\u5982\u679c\u4e24\u4e2a\u503c\u76f8\u7b49\uff0c\u8fd4\u56de <code>NULL<\/code>\uff0c\u5426\u5219\u8fd4\u56de\u7b2c\u4e00\u4e2a\u503c\u3002<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>SELECT NULLIF(10, 10);  -- \u8fd4\u56de NULL\nSELECT NULLIF(10, 5);   -- \u8fd4\u56de 10<\/code><\/pre>\n\n\n\n<h3 class=\"wp-block-heading\"><strong>6.3 <code>CASE<\/code><\/strong><\/h3>\n\n\n\n<p>\u6761\u4ef6\u8bed\u53e5\uff0c\u6839\u636e\u6761\u4ef6\u8fd4\u56de\u4e0d\u540c\u7684\u503c\u3002<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>SELECT CASE WHEN salary &gt; 50000 THEN 'High' ELSE 'Low' END FROM employees;<\/code><\/pre>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h2 class=\"wp-block-heading\"><strong>7. \u5b57\u7b26\u4e32\u8f6c\u4e49\u548c\u5904\u7406<\/strong><\/h2>\n\n\n\n<h3 class=\"wp-block-heading\"><strong>7.1 <code>MD5(string)<\/code><\/strong><\/h3>\n\n\n\n<p>\u8fd4\u56de\u5b57\u7b26\u4e32\u7684 MD5 \u54c8\u5e0c\u503c\u3002<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>SELECT MD5('password');  -- \u8fd4\u56de '5f4dcc3b5aa765d61d8327deb882cf99'<\/code><\/pre>\n\n\n\n<h3 class=\"wp-block-heading\"><strong>7.2 <code>ENCODE(bytea, encoding)<\/code><\/strong><\/h3>\n\n\n\n<p>\u5c06\u4e8c\u8fdb\u5236\u6570\u636e\u7f16\u7801\u4e3a\u6307\u5b9a\u683c\u5f0f\uff08\u5982 base64\uff09\u3002<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>SELECT ENCODE('Hello'::bytea, 'base64');  -- \u8fd4\u56de 'SGVsbG8='<\/code><\/pre>\n\n\n\n<h3 class=\"wp-block-heading\"><strong>7.3 <code>DECODE(string, encoding)<\/code><\/strong><\/h3>\n\n\n\n<p>\u5c06\u7f16\u7801\u540e\u7684\u5b57\u7b26\u4e32\u89e3\u7801\u3002<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>SELECT DECODE('SGVsbG8='::text, 'base64');  -- \u8fd4\u56de 'Hello'<\/code><\/pre>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h2 class=\"wp-block-heading\"><strong>\u603b\u7ed3<\/strong><\/h2>\n\n\n\n<p>PostgreSQL \u7684\u51fd\u6570\u529f\u80fd\u975e\u5e38\u5f3a\u5927\uff0c\u6db5\u76d6\u4e86\u4ece\u6570\u636e\u7c7b\u578b\u5904\u7406\u3001\u6570\u5b66\u8ba1\u7b97\u3001\u5b57\u7b26\u4e32\u64cd\u4f5c\u3001\u65e5\u671f\u65f6\u95f4\u3001\u805a\u5408\u51fd\u6570\u3001JSON \u6570\u636e\u5904\u7406\u7b49\u591a\u65b9\u9762\u7684\u9700\u6c42\u3002\u4e86\u89e3\u5e76\u638c\u63e1\u8fd9\u4e9b\u51fd\u6570\u80fd\u6709\u6548\u63d0\u9ad8\u6570\u636e\u67e5\u8be2\u548c\u7ba1\u7406\u6548\u7387\u3002\u66f4\u591a\u8be6\u7ec6\u5185\u5bb9\u8bf7\u5173\u6ce8\u5176\u4ed6\u76f8\u5173\u6587\u7ae0\uff01<\/p>\n","protected":false},"excerpt":{"rendered":"<p>PostgreSQL \u63d0\u4f9b\u4e86\u5927\u91cf\u7684\u5185\u5efa\u51fd\u6570\uff0c\u8fd9\u4e9b\u51fd\u6570\u652f\u6301\u5404\u79cd\u5e38\u89c1\u7684\u6570\u636e\u5904\u7406\u4efb\u52a1\uff0c\u5e2e\u52a9\u5f00\u53d1\u8005\u5b8c\u6210\u4ece\u5b57\u7b26\u4e32\u64cd\u4f5c\u5230\u6570 [&hellip;]<\/p>\n","protected":false},"author":1,"featured_media":2701,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[78],"tags":[],"class_list":["post-2700","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-postgresql"],"_links":{"self":[{"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/posts\/2700","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/comments?post=2700"}],"version-history":[{"count":1,"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/posts\/2700\/revisions"}],"predecessor-version":[{"id":2702,"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/posts\/2700\/revisions\/2702"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/media\/2701"}],"wp:attachment":[{"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/media?parent=2700"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/categories?post=2700"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/tags?post=2700"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}