sql的NULL和空字符串

类似于java的NULL和空字符串,NULL表示没有值,空字符串表示值为空字符串,完全不同的

SELECT NULL = NULL,NULL != NULL,NULL IS NULL,NULL IS NOT NULL FROM base_material LIMIT 1;

image.png

poi动态设置颜色

public class ExcelCellDynamicColor {
    private int col;//列数 从0开始
    private int startRow;//开始行数 从0开始
    //由内容来决定颜色 使用 HSSFColor 中的颜色
    private Map<String,Short> contentColorMap = new HashMap<>();
}
private static void setCellDynamicColor(HSSFWorkbook wb, ExcelCellDynamicColor cellDynamicColor){
    int sheetNum = wb.getNumberOfSheets();
    for (int i = 0; i < sheetNum; i++) {
        HSSFSheet sheet = wb.getSheetAt(i);
        int rows = sheet.getLastRowNum() + 1;
        for (int j = 0; j < rows; j++) {
            HSSFRow row = sheet.getRow(j);
            if (row == null)
                continue;

            HSSFCell cell = row.getCell(cellDynamicColor.getCol());
            //若单元格为空或行数小于开始行,则跳过
            if(cell == null || j < cellDynamicColor.getStartRow()){
                continue;
            }

            Short color = cellDynamicColor.getContentColorMap().get(cell.getStringCellValue());
            if(color != null){
                HSSFFont font = wb.createFont();
                HSSFCellStyle cellStyle = wb.createCellStyle();
                cellStyle.cloneStyleFrom(cell.getCellStyle());
                font.setColor(color);
                cellStyle.setFont(font);
                cell.setCellStyle(cellStyle);
            }
        }
    }
}